A pedestrian is dead this morning, after they were struck while reportedly crawling down Interstate 280 in San Francisco.

According to California Highway Patrol spokesperson Sergeant John Cardoso, calls reporting a pedestrian "crawling on the freeway in underwear" began to roll in at 6:18 this morning. By 6:20, the pedestrian had been struck and killed while in the southbound lanes of 280 near Alemany Boulevard.

It's unclear why the pedestrian was on the freeway, Cardoso says. According to CBS 5, "there were conflicting reports on whether the person killed was a woman or a man."

Police investigation of the crash closed three southbound lanes of the freeway and backed up traffic "for miles," Cardoso says. By 8 a.m. one lane had reopened, but he didn't have any information when the roadway would be completely cleared and said drivers should seek alternate routes.

There's also no word on the identity of the deceased, Cardoso says. It will require "fingerprint and dental records" to identify the dead pedestrian, Cardoso says, which "could take some time."