A tsunami generated by an offshore earthquake and underwater landslide might hit the U.S. state of California with virtually no warning, a newspaper report said on Wednesday.

Unlike Japan which suffered a major tsunami caused by a 9.0- magnitude offshore tremor last Friday, California does not have a subduction zone -- a fault where one plate slides under another in an earthquake -- off its coast, The Los Angeles Times said, quoting experts at the University of Southern California (USC).

The thrusting motion under the sea was what generated the 40- foot tsunami seen in Japan.

Southern California could see a significant tsunami caused either by a large earthquake off Alaska or by undersea landslides spurred by smaller earthquakes off California, while Northern California is at greater risk because of the Cascadia subduction zone, which runs along the Pacific Northwest coast, the report said.

But Southern California, unlike Northern California, has no tsunami measuring instruments off its coast because the area is considered to be at low risk, according to the report.

Tsunamis caused by underwater landslides off Southern California could reach as high as 40 feet, although they would be localized and quick to dissipate, said Costas Synolakis, director of the Tsunami Research Center at USC.

Quakes off Alaska and the Pacific Northwest could create 15- foot waves in Southern California and 25-foot tsunamis in the northern part of the state, California State Geologist John Parrish said.

That type of event is only expected to strike once in 2,000 or 3,000 years. But, as has happened in Japan, experts say all predictions may go out the window, the paper noted.

"Mother Nature is notorious for not obeying rules that we make, " Parrish was quoted as saying.

A quake off Alaska would give California six to nine hours lead time to clear the beaches before a tsunami struck, Parrish said. A temblor off the California-Oregon border, on the other hand, might give Northern California towns less than half an hour to prepare.

"That's not very much time, especially if it's two o'clock in the morning and you're trying to wake up a whole town of people and get them up the hill," he said.

USC researchers estimate that a tsunami created by an offshore quake could cost the region seven billion to 40 billion dollars from port closures alone.