Police officers secure the area after at least one person opens fire at a social services agency in San Bernardino, California, Dec 2, 2015. 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.[Photo/Agencies]

SAN BERNARDINO, Calif. - Gunmen opened fire on a holiday party on Wednesday at a social services agency in San Bernardino, California, killing 14 people and wounding 17 others before fleeing, authorities said.

As an intense manhunt for up to three suspects ensued, San Bernardino police reported one "suspect down" in an exchange of gunfire with officers but did not immediately confirm whether the individual was connected to the shooting.

The shooting rampage at the Inland Regional Center about 60 miles (100 km) east of Los Angeles marked the deadliest US gun violence since the massacre at Sandy Hook Elementary School in Newtown, Connecticut, in December 2012, in which 27 people, including the gunman, were killed.

San Bernardino Police Chief Jarrod Burguan said in a televised news briefing three hours after Wednesday's shooting that the suspects were believed to have made their getaway in a dark-colored sport utility vehicle.

A vehicle matching that description turned up at the shootout with police several hours later, city police spokeswoman Sergeant Vicki Cervantes. She said the number of wounded rose to 17.

With suspects at large, authorities ordered a security "lockdown" of all local schools, as well as city and county buildings, and area hospitals were placed on alert, Burguan said.