SAN JOSE . (AP) — San Jose residents remained on high alert Monday as authorities search for a serial arsonist they believe is responsible for nearly a dozen fires in the city within a week.

The fire department has reported 13 fires near downtown since Wednesday — 11 of them determined to be arson. The blazes usually occur during the early morning hours. Three fires alone were set early Sunday.

The targets have included homes and businesses and a church that was struck twice. More than 100 firefighters battled a massive 5-alarm blaze at a large vacant warehouse near U.S. Highway 101 on Thursday that delayed the morning commute and closed two nearby schools for the day.

No injuries have been reported.

Authorities have released a sketch of a person of interest in the case. Surveillance footage obtained by KTVU-TV (shows a man matching that description starting a fire on the porch of a home.

"When you see someone who is there who shouldn't be there, acting suspicious, going into peoples' driveways, knowing that they shouldn't be there — that is something you should report," San Jose Fire Capt. Cleo Doss told reporters Monday.

Residents in one area have taken to patrolling the neighborhood themselves. San Jose Fire Capt. Robert Brown said Monday that residents have been doing a better job of keeping the areas around their homes lit.

"There is a serious problem here in San Jose of someone who is destroying homes, and it's hurting everyone in San Jose," resident John Padilla told KTVU.

Ben Rodriguez told the station he had been awake all night keeping watch.

"This has felt really personal to me," Rodriguez said. "Whoever is doing this is just trying to tear this neighborhood up."

The local fire union is also helping out. They've put up a $10,000 reward for information that will lead to the suspect's arrest and conviction.