A tornado outbreak threatened parts of the South on Saturday, prompting forecasters to issue a rare “particularly dangerous situation” alert amid severe storms that damaged homes and a fire station, according to preliminary reports.

Millions of people were under tornado watches on Saturday in parts of Texas, Louisiana, Mississippi and Arkansas. Multiple more dangerous tornado warnings were also issued throughout Saturday. (The National Weather Service maintains a list of current tornado alerts, which change frequently as tornado threats develop and pass.)

The “particularly dangerous situation” wording is used in “rare situations when long-lived, strong and violent tornadoes are possible,” the weather service said. “Numerous” tornadoes are expected, forecasters said.

Multiple homes were destroyed between Alvin and Liverpool, Texas, when a possible tornado went through the area Saturday afternoon, according to a preliminary report cited by the Storm Prediction Center. In Montgomery County, mobile homes were damaged and a roof was ripped off a home.

The East Montgomery County Fire Department said in a post on Facebook that Station 154 had sustained “extensive damage” from a tornado, but said there were no injuries reported.

One tornado is suspected to have touched down in Katy, Texas, in the Houston metro area, according to videos posted to social media by AccuWeather and other meteorologists.

Travelers beware: Severe weather forecast says storms, tornadoes and snow

In Dermott, Arkansas, which was under a severe thunderstorm warning Saturday morning, forecasters said: “This destructive storm will contain baseball sized hail!”

The storms come after a previous round of weather hit parts of Texas and Louisiana on Thursday with multiple tornadoes and severe thunderstorms, AccuWeather reported.

Severe weather warnings and watches map

What’s a tornado watch, warning?

A tornado watch happens when weather conditions are prime to spawn tornadoes, and they alert people to be ready to act quickly in and around the area of a watch.

A tornado warning means a tornado has been spotted or is indicated by weather radar, and there is imminent danger to life or property. During a tornado warning, people should seek shelter in interior rooms on the lowest floors of study buildings, and keep away from windows.

(This story has been updated to add new information and to correct a misspelling/typo.)