At least one person opened fire at or near a state social services agency in the Southern California city of San Bernardino on Wednesday and as many as 20 people were wounded, authorities said.

The San Bernardino Police Department said on Twitter that it had "confirmed 1 to 3 possible suspects" and multiple victims in the shooting. The agency called it an "active shooter" incident.

The San Bernardino Fire Department said in a tweet that it was responding to reports of 20 victims.

The shooting took place at the Inland Regional Center, one of 21 facilities serving people with developmental disabilities run by the state, said Nancy Lungren, spokeswoman for the California Department of Developmental Services.

Lungren said she did not yet have more information.

Television images on CNN showed people being evacuated from the building, their arms raised, as triage stations were set up outside. Police and SWAT teams were seen surrounding the building.

A police spokeswoman told the Los Angeles Times that the suspects were heavily armed and possibly wearing body armor.

A spokeswoman from nearby Loma Linda Medical Center said the hospital was expecting patients momentarily. "We're all kind of on standby right now - it could be any minute," spokeswoman Briana Pastorino said.