Police stopped the SUV they were in, which led to a pursuit and shoot-out.
San Bernardino police chief Jarrod Burguan also said authorities found what they believe is an explosive device at the Inland Regional Centre in San Bernardino where the shooting, which killed at least 14 people and wounded more than a dozen others, happened. Bomb squads were working on it.
The FBI said it was possible that the shooting was an act of terrorism and Mr Burguan said the suspects were wearing “assault-style clothing” and were armed with assault rifles and handguns.
A person seen running near the gun battle between police and the suspects has been detained, but Mr Burguan said it was not clear if that the person was connected to the shooting.
Up to three gunmen were thought to have carried out yesterday’s attack, opening fire at the centre “as if they were on a mission”. A police officer received minor injuries in the shoot-out.
Hours later, police riddled a black SUV with gunfire several miles away and one person lay motionless in the street with a gun nearby. Officers appeared to remove a second person from the vehicle.
Police later began searching a home in Redlands after half a dozen vehicles carrying helmeted officers arrived and an armoured vehicle parked outside a row of houses.
It was the nation’s deadliest mass shooting since the attack on Sandy Hook Elementary School in Newtown, Connecticut, in December 2012, that left 26 children and adults dead.
Police shed no light on a motive for the massacre, which came just five days after a gunman opened fire at a Planned Parenthood family planning clinic in Colorado, killing three.
“They came prepared to do what they did, as if they were on a mission,” San Bernardino police chief Jarrod Burguan said, noting the attackers carried long guns - which can mean rifles or shotguns.
Witnesses said several people locked themselves in their offices, desperately waiting to be rescued by police, after gunfire erupted at the Inland Regional Centre in San Bernadino, which serves people with developmental disabilities. Some people phoned their loved ones and whispered to them what was going on.
The attack took place in a conference area where the San Bernardino County Department of Public Health was renting space to hold a banquet, said Marybeth Feild, president and CEO of the centre. The building has at least 25 employees as well as a library and conference centre.
FBI agents and other law enforcement authorities converged on the building and searched rooms for the attacker or attackers, but it was feared that they had escaped.
Ten of the wounded were taken to hospital in a critical condition and three were in a serious condition. Police warned that the numbers of dead and wounded were early estimates that could change.
No weapons were recovered at the centre, though authorities were investigating unidentified items in the building and brought in bomb squads.
Sergeant Cervantes said there were reports from witnesses of one to three gunmen.
As the manhunt went on, stores, office buildings and at least one school were locked down in the city of 214,000 people about 60 miles east of Los Angeles, and roads were blocked off.
Triage units were set up outside the centre and people were seen being wheeled away on stretchers. Others walked quickly from a building with their hands up. They were searched by police before being reunited with loved ones.
US president Barack Obama was briefed on the attack by his homeland security adviser.
He said it was too early to know the shooters’ motives, but urged the country to take steps to reduce the frequency of mass shootings. He told CBS that stricter gun laws, including stronger background checks, would make the country safer.
“The one thing we do know is that we have a pattern now of mass shootings in this country that has no parallel anywhere else in the world, and there’s some steps we could take, not to eliminate every one of these mass shootings, but to improve the odds that they don’t happen as frequently,” Mr Obama said.
The shooting sounded like “an organised plot” and preliminary information seems to indicate that “this is personal, and there seems to suggest some element of revenge and retaliation”, said Erroll Southers, director of Homegrown Violent Extremism Studies at the University of Southern California and a former FBI agent.
“What it says to me, it’s someone who’s familiar with the facility, it’s someone who knew exactly what room they were going to go to, they knew exactly which way they needed to escape.
“They’ve done their homework, they know what the response time in this jurisdiction.”
Terry Petit, whose daughter works at the centre, where social workers find jobs, housing, transportation and provide programmes for people who have disabilities such as autism, cerebral palsy and epilepsy, received a text from her saying she was hiding in the building after hearing gunshots.
Mr Petit choked back tears as he read the text, which said: “People shot. In the office waiting for cops. Pray for us. I am locked in an office.”
Sherry Esquerra was searching for her daughter and son-in-law, both of whom work at the centre. She said her daughter helped “very disabled” children and “gets all the services she possibly could for these kids”.
“I just don’t understand why somebody would come in and start shooting,” Ms Esquerra said. She last saw her daughter at Thanksgiving and planned to see her on Friday. When she called her phone she got “nothing. I just get her message. Straight to voicemail”.
Marcos Aguilera’s wife was in the building when the gunfire erupted. He said a shooter entered the building next to his wife’s office and opened fire.
“They locked themselves in her office. They seen bodies on the floor,” he said, adding that his wife was able to leave the building unharmed.
The social services centre has two large buildings that require a badge to enter, said Sheela Stark, an Inland Regional Centre board member. But the conference room where many public events take place, including the banquet yesterday, was usually left open when visitors were expected.
David Bowdich, assistant director of the FBI’s field office in Los Angeles, said one possible motive for the attacks was workplace violence and another terrorism.