US police launched a manhunt Wednesday for a Californian man suspected of killing his wife and two young daughters, and warned that he was armed and dangerous.

Shane Franklin Miller allegedly shot his 34-year-old wife Sandy and daughters Shelby, eight, and 4-year-old Shasta on Tuesday in Shingletown, 230 miles (370 km) north of San Francisco.

"Miller is considered armed and dangerous, possibly having access to a cache of weapons," said Shasta County Sheriff's Office, adding that they were pursuing leads in northern California, while declaring a nationwide manhunt.

The 45-year-old "is a suspect in the triple homicide of his wife and two daughters," it added in a statement.

Several nearby schools were ordered onto lockdown, according to the regional Times-Standard newspaper, which said the suspect pulled his daughters out of their local public schools three to four weeks ago.

The girls had been transferred to a local charter school and begun homeschooling, the paper said.

Don Aust, a local school superintendent, said: "I never saw anything like that. We're a small enough school -- one teacher per grade -- I can tell when somebody's going through some kind of problem.

"Nothing had a red flag for me."