SAN FRANCISCO -- A gunman opened fire on Highway 280 in San Francisco early Monday, wounding several people and forcing the shut down of the southbound lanes of the freeway for several hours, CBS San Francisco reports. The California Highway Patrol said they and the San Francisco police received calls reporting the shooting at around 3 a.m. on southbound 280 at Alemany Boulevard in San Francisco.

The California Highway Patrol reports that there were "several victims" in the shooting but there was no word on their conditions.

"There were several victims — anywhere between 3 to 6," said CHP officer Francisco Garcia. "We are collecting evidence and interviewing the victims."

#BREAKING: Shooting shuts down all lanes of SB 280 at Alemany in #SanFrancisco. @CHPSanFrancisco says "several victims" reported at this time, no word on conditions of the victims. @JessicaFloresTV heading to the scene. pic.twitter.com/oqZDhxLGxZ — KPIX 5 (@CBSSF) January 15, 2018

Arriving officers did not locate any victims or the shooter, but did find shell casings on the freeway.

Get Breaking News Delivered to Your Inbox

All southbound lanes were closed for about two hours.

The motive for the shooting remains under investigation.