The bedrock of the financial system trembled on Friday, with government bond yields rising sharply as the chaotic rollout of tariffs shook investors’ faith in the pivotal role played by the United States in the financial system.

U.S. government bonds, known as Treasuries because they are issued by the U.S. Treasury, are backed by the full faith of the American government, and the market for Treasuries has long been deemed one of the safest and most stable in the world.

But the Treasury market’s erratic behavior all week has raised fears that investors are turning against U.S. assets as President Trump’s trade war escalates.

The yield on a 10-year Treasury, which underpins corporate and consumer borrowing and is arguably the most important interest rate in the world, rose roughly 0.1 percentage points on Friday. Friday’s rise added to sharp moves throughout the week that have taken the yield on the 10-year Treasury from less than 4 percent at the end of last week to around 4.5 percent this week.

These increases may seem small, but they are large moves in the Treasury market, prompting investors to warn that Mr. Trump’s tariff policies are causing serious turmoil. It matters to consumers as well. If you have a mortgage or car loan, for example, then the interest rate you pay is related to the 10-year yield.

Ten-year treasuries are also considered a safe haven for investors during time of volatility in the stock market, but this week’s sharp rise in yields have made this market unusually perilous.

Yields move in the opposite direction to prices. So as yields have been rising unexpectedly, investors around the world that hold trillions of dollars of Treasuries are seeing their value suddenly decline.

Rising yields on the 30-year long bond have also been historic, analysts said. This bond is considered a particular refuge for pension funds and insurance companies, because they have liabilities that stretch into the future, so they need assets that match that.

“This is not normal,” Ajay Rajadhyaksha, global chairman of research at Barclays, wrote in a report on Friday. Grappling for an explanation, Mr. Rajadhyaksha pointed to speculation by Asian investors who are selling in response to tariffs, as well as the possible unwinding of highly leveraged bets in the Treasury market. “Whatever the reason, right now, bond markets are in trouble,” he said.

The yield on the 30-year Treasury bond rose 0.44 percentage points this week, trading roughly flat on Friday. The movement signaled a sharp shift in demand for the long bond. The Federal Reserve fixes a few very short-dated interest rates that then ripple out across financial markets. But the further away from the Fed’s rates you go, the less impact the central bank has.

“Once you get to the long end, they aren’t really in the picture,” said Matt Eagan, a portfolio manager at fund manager Loomis, Sayles & Company. “There are fewer natural buyers in that market. Small changes to supply and demand can lead to big swings.”

Another worrying sign this week has been the decline in the U.S. dollar, which tumbled 0.8 percent against a basket of currencies representing its major trading partners on Friday. Every currency of the group of 10 nations rose against the dollar, further pointing to a move away from U.S. assets.

A weaker dollar at the same time as government bonds and stocks are selling off is a rare combination, given the dollar’s role as the global financial system’s safe haven.

Despite the monthslong slump in the stock market, which is approaching a bear market, it was the bond market looking “queasy” that Mr. Trump said prompted him on Wednesday to pause the worst of his tariffs for most countries.

“The big risk elephant in the room is the Treasury market,” Mr. Eagan said.

For investors, the moves echoed the wild price swings from the pandemic-induced sell-off in March 2020 and before that, a bout of volatility in September 2019. Those events spooked investors and prompted rapid intervention from the Federal Reserve to stabilize the market.

This time, the Fed is in a trickier position. The inflationary effect of tariffs warrants the central bank keeping interest rates high. But it would be more supportive to financial markets and economic growth to lower interest rates, something the central bank has so far resisted doing.

On Friday, a widely watched measure of consumer sentiment fell to its lowest level in roughly three years. Expectations for where inflation will be in 12 months time soared, underscoring the Fed’s challenge.

In the meantime, this week’s chaotic implementation, then partial reprieve, on global tariffs, followed up by an escalating trade war between the U.S. and China, has left global investors unsure of relying on the Treasury market, or even the U.S. dollar, as a source of safety and stability.

Foreign investors are among the biggest holders of U.S. government debt. Japan is the largest, based on official data, with more than $1 trillion worth of U.S. Treasury debt. The next largest in China, which holds $760 billion of Treasuries, having already reduced its holdings by more than a quarter of a trillion dollars since 2021.

“WAKE UP PEOPLE,” Andrew Brenner, a veteran bond trader and head of international fixed income at National Alliance Securities, wrote in a brief email. “THIS IS FOREIGN MONEY EXITING THE TREASURY MARKET DUE TO TARIFF POLICIES.”

Some analysts and investors fear that a more rapid pace of selling by foreign investors could push U.S. Treasury yields, and with them U.S. interest rates, even higher.

“Picking fights with major trading partners who also finance your debt becomes especially risky with a wide fiscal deficit and no credible plan to rein it in,” Mr. Eagan said.

Alternatives around the world are also benefiting. Germany has recently announced plans to invest in its military, financed through new debt. The country’s bond market is seen as Europe’s benchmark and is often compared to the Treasury market. As concerns about tariffs initially took hold last week, the spread, or difference, between the yield on 10-year German bunds and 10-year Treasuries shrank, as investors sought out the U.S. haven.

That has quickly reversed.

The head of the United Automobile Workers union voiced partial support on Thursday for the Trump administration’s tariffs, saying targeted duties on other countries could help bring some manufacturing jobs back to the United States.

But the union’s president, Shawn Fain, described President Trump’s across-the-board global tariffs as “reckless.” In an address to U.A.W. members that was streamed on YouTube and other social media, he also strongly criticized the administration for firing federal workers and slashing key government agencies, and accused it of violating the civil rights of students and others.

“We support use of some tariffs on automotive manufacturing and similar industries. We do not support tariffs for political games about immigration or fentanyl,” Mr. Fain said. “We do not support reckless tariffs on all countries at crazy rates.”

The address appeared aimed at distancing the union leader from Mr. Trump. In previous weeks, Mr. Fain praised the White House’s tariff plans and faced some criticism for moving closer to an administration that often shows hostility to organized labor. He campaigned frequently and enthusiastically last year for former Vice President Kamala Harris, the Democratic presidential nominee, often rousing crowds by referring to Mr. Trump as a “scab.”

“We are not aligning everything we do with the Trump administration,” Mr. Fain said on Thursday. “We are negotiating with the Trump administration.”

Mr. Fain used the address to repeat familiar claims that free trade agreements — in particular, the North American Free Trade Agreement — allowed corporations to move U.S. factories and jobs to low-wage countries. He said some 90,000 factories in the United States closed in the last 30 years, hollowing out once thriving manufacturing cities like Flint, Mich., and Gary, Ind.

While he blamed both Democrats and Republicans for supporting policies that have hurt U.S. manufacturing, Mr. Fain said the resulting “pain and anger” had led many workers who traditionally supported Democrats to gravitate toward Mr. Trump.

“We have to end this free trade disaster, and we don’t care whether it’s a Republican or Democrat who does it,” he said.

Mr. Fain said that General Motors, Ford Motor and Stellantis had excess manufacturing capacity in their U.S. plants and could create thousands of auto assembly jobs by making full use of them.

He added that he disagreed with “90 percent of what the Trump administration is doing,” especially the cuts at the National Institutes of Health that have disrupted research into cancer and other diseases.

“We’ve seen the destruction of bargaining rights for one million federal workers. We’ve seen an attack on the National Labor Relations Board and the illegal firing of a board member,” he said. “We’ve seen the attacks on Social Security and Medicare and Medicaid, programs that millions in the working class depending on.”

Mr. Fain did not mention Elon Musk, who as an adviser to Mr. Trump has been leading efforts to fire tens of thousands of federal workers and to make deep cuts at agencies including the Department of Education and Department of Veterans Affairs. Mr. Musk, the chief executive of Tesla, has strongly opposed U.A.W. efforts to organize Tesla’s workers in the United States.

Mr. Fain noted that Mahmoud Khalil, the recent Columbia University graduate who was arrested by federal immigration agents last month, had once been a student instructor represented by the U.A.W. Grant Miner, a graduate student who was expelled by the university last month, is president of U.A.W. Local 2710, which represents Columbia student workers.