Health officials in California are assuring residents of the state that nuclear radiation from Japan's damaged reactors pose little danger to the US.
"What we're being told is that there is no threat to California at this time," California Department of Public Health spokesman Mike Sicilia was quoted as saying by the Los Angeles Times.
"It is a matter of distance. Dangerous radioactivity could not cross the 5,000 miles of the Pacific without petering out".
Nuclear radiation from Japan's damaged Fukushima reactors could reach California within days but experts say the amount that makes its way across the ocean should pose no danger.
California and federal health officials have opened hotlines to answer questions about possible radiation risks, the report added.
Atmospheric scientist with the California Air Resources Board in Sacramento Tony VanCuren said only a "catastrophic release" of radiation would be able to carry dangerous levels across the ocean.
At that rate, it would take five to 15 days for particles to reach California.
Authorities in California have also tried to reassure the people that the kind of nuclear crisis facing Japan was highly unlikely at the state's two nuclear power plants.
The state's San Onofre nuclear power plant was built to withstand a 7.0 magnitude quake.
Quake experts have said the chance of a 9.0 quake and tsunami occurring in the southern half of California were highly unlikely.
"There's no offshore fault in any of Southern California that's exactly like the one that broke in Japan," the LA Times quoted Thomas Jordan, director of the Southern California Earthquake Center at USC, as saying.