Updated

Four people were injured and the busiest border crossing in the U.S. was closed to northbound vehicle traffic for hours Tuesday after federal agents fired shots across nine lanes of traffic to stop three vans suspected of smuggling illegal immigrants from Mexico, authorities said.

The 74 people crammed into the vans were taken into federal custody.

Details remained sketchy, but San Diego police spokesman Lt. Kevin Rooney said the van drivers tried to storm past inspectors at the San Ysidro port of entry — which connects San Diego and Tijuana, Mexico — and make their way into the U.S. without stopping.

Two U.S. Immigration and Customs Enforcement agents and a Customs and Border Patrol agent fired their guns to try to stop them, he said. There was no return fire.

"It was human smuggling, definitely," ICE spokeswoman Lauren Mack said.

The shootout occurred over nine of the 24 northbound traffic lanes, said Monica Munoz, a San Diego police spokeswoman.

The vans pulled into the same lane, and the first driver gave his license to a border agent, Rooney said. When the agent stepped back into the booth to run the license, all three vans drove quickly into the U.S. side.

"They got caught in traffic, and the last one tried to back up. The other two drove wildly looking for an open space to drive through," Rooney said. "That's when they encountered the three agents, who all ended up firing from different vantage points."

Three people in the vans where injured by gunfire, said San Diego Fire Department spokesman Maurice Luque. The lead van smashed into another vehicle, injuring a fourth person.

One shooting victim was still in critical condition at a hospital Tuesday night. The others were expected to recover.

The shooting will be investigated by the San Diego Police Department's Homicide Unit.

The border crossing's northbound lanes were closed after the 3:30 p.m. incident, creating a massive rush-hour traffic jam as drivers on the Tijuana side were turned back. Motorists were told to make their way through Tijuana's crowded streets to San Diego's only other border crossing at Otay Mesa, about five miles to the east.

Eight northbound lanes were reopened at about 7:30 p.m.

About 40,000 vehicles enter the U.S. each day at San Ysidro.

Michael Stray, 56, of Palm Springs, had spent the day in Tijuana and was one of those caught in the traffic as he and his private driver tried to return to the United States at about 4 p.m.

Stray said the driver spent about an hour going in circles trying to reach the border before he found an open street. Stray was able to cross at a pedestrian crossing about 5:15 p.m.