A disgruntled worker opened fire on Wednesday at a Northern California cement plant and quarry, killing three people and injuring six others, four or five of them critically, police said.

The gunman, identified as Shareef Allman, was also suspected of shooting a Hewlett Packard worker during an attempted carjacking a short time later in the HP parking lot, Santa Clara County Sheriff's spokesman Sgt. Jose Cardoza said.

Witnesses told detectives that a man matching Allman's description fled the scene of the second shooting on foot, Cardoza said, and authorities were looking for him in nearby neighborhoods.

We believe him to still be in the area. Several tactical teams are conducting yard-to-yard searches, Cardoza said.

Witnesses told police that Allman had arrived at a safety meeting at the Lehigh Southwest Cement Permanente Plant in Cupertino at about 4:30 a.m. armed with a handgun and rifle, and opened fire on roughly 15 of his co-workers, Cardoza said.

He was unhappy and disgruntled, according to witnesses and victims, Cardoza said. We don't know if it was work or family issues.

Witnesses and victims said Allman, in his 40s, later fled in a dark colored vehicle, Cardoza said.

He should be considered armed and dangerous, Santa Clara County Sheriff Laurie Smith told reporters at a press conference.

Police have recovered four guns used in the attack, one of which was a fully-loaded AK-47 or SKS assault rifle, roughly 150 yards from Allman's tan Mercury Cougar, a sheriff's deputy at the scene said, declining to be named.

SWAT TEAM

The deputy said Allman was scared away from the HP parking lot by another person in the lot. That woman got out of her car, startling Allman, who fired shots at and hit her car before fleeing on foot, he said.

A truck full of SWAT team members in full riot gear was seen entering the scene of the HP parking lot shooting.

The cement plant is part of Germany's HeidelbergCement AG, the world's No. 3 construction materials group.

We are shocked and saddened by this morning's events, said Dan Harrington, President and CEO of Lehigh Hanson, in a statement e-mailed to the media.

Our thoughts and prayers are with the victims and their families. I have committed the company's resources to assist our affected employees during this difficult time.

U.S. Representative Michael Honda, whose district includes Cupertino, said in a statement: Today is a somber day. Our close-knit community was violently attacked, and we will continue to feel the shocks of this violence for some time.

One of the victims from the cement plant shooting was treated and released from a local hospital. The conditions of the other five people were not immediately available.

According to the deputy at the scene, one of the victims, now in critical condition, was shot in the face outside of the meeting room.

The woman shot in the attempted carjacking, whose name was not released, was in fair condition at Santa Clara Valley Medical Center.

A spokesman for HP said that its campus had been closed because of the shooting and the company was working with local authorities. He confirmed that its contract employee was in safe, stable and noncritical condition.