San Francisco police spokesman Gordon Shyy says several urgent calls reported that someone had driven into the bay in front of many witnesses at Marina Green at about 5 p.m. Friday.
Witnesses tell ABC7 News they heard the engine racing as the van went by at about 20 mph into the water. They say it got so far out because it floated for a while.
Police say people from a civilian boat were trying to help the occupants of the van or SUV that was partly submerged. They were soon joined by divers from the police and fire departments.
"We were there before the police, before fire," said Vince Casalaina with Red Bull Racing. "We were at the Golden Gate Yacht Club, getting ready for a party tonight, and we heard some yelling from over on the sea wall at the Marina Green. We didn't know what was going on at first, but then we saw the van as it started to float out, away from shore. At which point, my team got in our boat and went out to see what we could do. Three of the guys jumped in the water and tried to break the windows but couldn't get the glass to break enough to get anyone out. So they were actually on the van as it sank."
Casalaina said it took about four to five minutes from the time the van went into the water, to the time it went under.
U.S. Coast Guard boats and a helicopter are searching the water.
Shyy didn't immediately know how many people were inside or have any immediate word on injuries.
Stay with ABC7 News for the latest on this developing story.
(ABC7 news contributed to this report)