SAN PABLO, Calif. -- Police in San Pablo are investigating a pair of early morning vehicle fires, California Highway Patrol Officer John Short said.

The fires were reported at around 2:15 a.m. in the 2100 block of Vale Road near San Pablo Avenue, where two vehicles appear to have been set ablaze at the same location, Short said.

Whether these latest fires are connected to at least 20 others set in Contra Costa County since Oct. 31 is under investigation.

Earlier this week, investigators determined that two Tuesday vehicle fires were arson, but they have not yet confirmed that they are linked to the other 11 fires in Richmond and El Sobrante that burned 17 vehicles, Contra Costa County Fire Investigator Victor Massenkoff said.

He said investigators now believe that the first fire in the series was set on Oct. 31 on Ridge View Circle in El Sobrante, where one vehicle was burned.

Six more fires that burned 12 vehicles were set in Richmond and El Sobrante in the early morning hours of Nov. 4. And three more fires were set the night of Nov. 7, burning three vehicles. The eleventh fire was set in the early morning of Nov. 10 in El Sobrante, according to the fire district.

Investigators have received about a dozen tips through the arson tip line and are actively following leads, but so far have not identified any potential suspects, Massenkoff said.

He said investigators believe the fires are the work of one person, but have not ruled out the possibility that other people could be involved. He also said that the victims have so far had no connection to each other and appear to have been chosen at random.

While none of the fires have spread to homes, many of them were set in cars parked in driveways within one to two feet of homes where families were sleeping, Massenkoff said. In several cases, residents didn't even know anything was happening until firefighters woke them up to tell them to get out of their houses.

He said he couldn't discuss the method used to set the fires, but said that most of them had been lit inside vehicles that had been left unlocked or with a window down.

There have been no witnesses to any of the fires and investigators are asking residents to be vigilant.

People should make sure their vehicles are locked, install security lighting and talk to their neighbors, Massenkoff said. He said anyone who sees anything out of the ordinary should call the arson tip line at (866) 50-ARSON.

Investigators from the Contra Costa County Fire Protection District, Richmond Fire Department, Richmond Police Department, Contra Costa County Sheriff's Office and San Pablo Police Department are sharing information and working together to find the person or people setting the fires. State and federal law enforcement agencies are also providing support in the investigation, according to the fire district.