Throngs of passengers anxious to get on their way surged into Heathrow Airport in London on Saturday, a day after a power blackout closed the airport and forced thousands to delay their trips.

As information boards flickered back to life, an army of extra airport staff members, dressed in purple, sprang into action to help people as they walked through the terminal doors.

Ganesh Suresh, a 25-year-old student who was trying to get home to Bangalore, India, was among those who secured a coveted seat on a Saturday flight. After his Air India flight was canceled, his parents booked new tickets on Virgin Atlantic, while he spent the night at a friend’s place in Birmingham, England.

“I was so eager to get back,” Mr. Suresh said. He sheepishly admitted to yelling at his parents in frustration during the height of the shutdown chaos. “I might apologize to them when I get back.”

Travelers, diverted or rebooked, arrived early, with trains and other transport routes to the airport reopened. A day earlier, the airport’s roads were empty except for police cars.

A Heathrow representative said on Saturday that the airport was “open and fully operational,” adding that the extra flights on the day’s schedule could accommodate 10,000 extra passengers. At the airport, information boards showed that most flights would leave on time, but the snaking lines at ticketing counters signaled that many travelers were in for more frustrating delays.

More than a thousand flights were diverted on Friday, wreaking havoc on more than a quarter of a million people’s travel plans, Cirium, an aviation data company, estimated.

Some travelers chose not to wait for a flight out of Heathrow. Denyse Kumbuka had lingered in the dimmed Terminal 2 for as long as she could on Friday, spending hours on a bench trying to find her way back home to Dallas.

Then her husband found a seat for her on a flight via Austria. She navigated the London Underground rail system to St. Pancras International train station and got a train to Paris. After spending the night on another bench at Charles de Gaulle Airport, she took an early flight to Vienna, then connected to Dallas on Saturday morning.

“I feel like the mom in ‘Home Alone,’” she said in a text message, referencing the exhausting journey depicted in the 1990 film.

A Heathrow representative said significant delays were expected in the coming days as airlines tried to return their planes to their usual schedules.

Mars Gonzalez, 32, and Olivia Hawthorne, 24, were stuck in the lingering aftermath. They were only meant to transfer at Heathrow on Saturday on a trip from Barcelona to Dallas, with another stop at Kennedy Airport in New York. Instead, they found themselves wandering out of the arrivals gate at Terminal 5 for an unplanned stay in London.

When news of the fire broke, Ms. Gonzalez said she called American Airlines, who assured her that the flight, operated by British Airways, would take off on Saturday as scheduled. But when they got to Heathrow, delays stretched from hours to days, with the next available flight on Tuesday.

“We spoke to like six different people who were just redirecting us to other people,” said Ms. Hawthorne.

For Stephen Delong, 74, and Lesley Scott, 73, the long line at the ticketing office turned out to be the smoothest part of their redirected travel.

“You have to come here; you have to talk to someone,” Mr. Delong said. “The online service just doesn’t work.”

The couple had just learned that in place of their original direct flight from London to Halifax, Air Canada would be rerouting them via Toronto, adding more than 15 hours to their travel time thanks to a long layover. And they would have to spend another night in London because flights on Saturday were all booked. The shutdown had already caused them to miss their grandson’s eighth birthday on Friday.

“You can’t get angry about it,” Mr. Delong said. “It would feel different if somebody blew up the generator.”

The police were still investigating what had caused the fire at the substation in western London that cut power to Heathrow.

John Yoon contributed reporting.