UPDATE: At about 1:30 p.m., a citizen reported seeing an abandoned LAPD vehicle at the side of the westbound 210 Freeway approaching Interstate 5. A subsequent LAPD roll call showed two officers were missing. Deputies from the SCV and La Crescenta stations searched the freeway and found nothing. The LAPD then said the two officers were accounted for; their radios weren’t working. It was determine to be a false alarm.

Sheriff’ deputies throughout Los Angeles County are on high alert after an officer-involved shooting Thursday morning.

A “blue alert” was issued after Christopher Dorner, a 33-year-old man allegedly was “involved in multiple shootings with multiple agencies in the Riverside area,” according to a California Highway Patrol statement.

“We just have all of our units are two-man units today, and we’re sending two units to every call,” said Lt. Mark Hershey of the Santa Clarita Valley Sheriff’s Station.

A blue alert is a term law enforcement uses for threats against officers, according to law enforcement official.

Local CHP officials said they would be proceeding with caution, but not doing anything out of the ordinary, in response to the alert.

“CHP we always uses the utmost in officer safety, so we’re not taking any extra precaution, we do that every day,” said Officer Lesnet of the California Highway Patrol’s Newhall Station.

The suspect was last seen driving a grey Nissan Titan, license plate 8D83987, there’s also a ski rack on top of the vehicle.

An intensive  manhunt is under way for the hulking ex-LAPD cop suspected of carrying out a twisted plan — detailed in a chilling online manifesto — to settle old grudges by executing police officers and their families.

Dorner, a 270-pound former Navy reservist who was tossed off the police force in 2008, is wanted for the double murder of a retired captain’s daughter and her fiancé in Irvine, Calif., on Sunday.

Authorities told NBC Los Angeles they also believe he’s behind Thursday’s ambushes of cops searching for him in Riverside and Corona, Calif. One officer was killed and two others were wounded in those attacks.

“I never had the opportunity to have a family of my own, I’m terminating yours,” Dorner wrote in his rambling 20-page manifesto, addressing LAPD officials he blamed for ruining his career.

“Look your wives/husbands and surviving children directly in the face and tell them the truth as to why your children are dead.”

The city of Los Angeles was put on tactical alert and the state’s highway patrol issued a “blue alert” for nine Southern California counties for Dorner, described as “armed and extremely dangerous,” while freeway signs urged motorists to call 9-1-1 if they see the suspect’s vehicle — a black 2005 Nissan Titan truck, according to the Los Angeles Times.

Dorner, 33, was a lieutenant in the Navy Reserves from 2002 until this week, and earned a ribbon for rifle marksmanship and a medal for pistol expertise. He joined the Los Angeles Police Department in 2005 and was fired for making false statements in 2008.

In an 11,300-word blueprint for vengeance, Dorner claimed that he was punished for accusing his field training officer of brutalizing a mentally disabled man and raged that his ouster had ruined his name.

“The attacks will stop when the department states the truth about my innocence, PUBLICLY!!!” he wrote. A cached version of the online manifesto was obtained by NBCLosAngeles.com.

During his internal LAPD review, Dorner was represented by union lawyer Randy Quan, a retired captain — and Quan’s daughter was the first victim.

Attorney General Kamala D. Harris Expresses Condolences Over Death of Riverside Police Officer