As radiation from the damaged nuclear plants in Japan is expected to reach California soon, state and local officials rushed to calm the public on Thursday that the radiation would not pose any threat.

Amid reports that winds could deliver a "radioactive plume" to the West Coast as early as Friday, California and Los Angeles County officials called a news conference to calm down public fear.

"We understand people's concerns," said Howard Backer, interim director of California's Public Health Department. "Radiation is scary stuff. It can have devastating effects in high does, but we also need to remember that radiation is part of our natural environment."

There was no health risk despite reports that radiation from the Fukushima nuclear power plant in Japan might reach Southern California by Friday, Backer said.

Any radiation emitted by the failing Japanese nuclear reactors would dissipate during the 5,000-mile (8,000-km) journey across the Pacific Ocean, Backer said.

"We do not anticipate any amount of radiation that would cause any health effects," he said. "... We're 5,000 miles away, which would have a major dispersal effect on any radiation."

Even if increased radiation is detected by monitors in California, it would be the equivalent to "natural background levels" in air and soil, he said.

Dr. Jonathan Fielding, Director of Los Angeles County's Public Health Department, said "the biggest health impact is the psychological impact."

"When people hear the word 'radiation,' it creates fear that's disproportionate to the threat," he said.

Fielding downplayed some media reports about U.S. airline passengers being found to have elevated radiation levels, noting that such occurrences are common and can often be attributed to causes such as recent medical procedures or even possession or exposure to clay-based products such as ceramic tile or cat litter.

Chuck Pickering, chief safety officer at City of Hope hospital in Los Angeles, told local TV station KCAL9 that people should go about their lives normally without fear of radiation.

"The amount of radiation we are all exposed to every day, every year, varies quite a bit around the world," he said. "Even in Denver, the radiation levels -- the population of Denver is exposed to twice what we would get here in Los Angeles. So the amount of radiation someone might be exposed to we expect to be actually much less than if you went and lived in Denver for a period of time."

Also on Thursday, the U.S. Customs and Border Protection issued a statement, saying that it had been paying closer attention to U.S.-bound flights from Japan since Tuesday, although it did not give specifics.

According to the agency, no dangerous levels of radiation had been detected among any passengers or cargo.

Meanwhile, state and local health officials stressed that people should not be ingesting potassium iodide, which is believed to prevent the body's absorption of radiation, because of the possible side effects such as nausea, rashes and possible severe allergic reactions.

"Residents who ingest potassium iodide out of concern of possible exposure from this situation are doing something which is not only ineffective, but could also cause side effects," Fielding said earlier.

"If a need should arise for residents to start taking potassium iodide to guard against effects of radiation exposure, the Los Angeles County Public Health Department -- along with other local, state and federal agencies -- will inform the public. We do not anticipate this need."

Officials said if people want to be prepared, they should take the opportunity to put together an earthquake kit that includes food, water, medications and a battery-operated radio.