A Los Angeles Police Department tactical unit responded Sunday to reports that someone may have opened fire near a pro-President Donald Trump rally, authorities said.

In a statement, the department said that three suspects had barricaded themselves inside an apartment building in Woodland Hills, northwest of downtown Los Angeles.

Police said the shooting occurred shortly after 11:30 a.m., when a large caravan of cars were amassed on Ventura Boulevard. A woman who wasn’t part of the rally was driving past it and said her tire went flat after she heard what sounded like gunshots, authorities said.

The tire appeared to have been damaged by a bullet or a bullet fragment, the statement said.

A SWAT team responded to an apartment building where police said three suspects had barricaded themselves inside, the statement added. The department later said SWAT officers entered one of the apartments, but the suspects were gone, and investigation is continuing.