Radioactive fallout from Japan's crippled nuclear plant has reached Southern California but the first readings are far below levels that could pose a health hazard, a diplomat said Friday.

The diplomat, who has access to radiation tracking by the U.N.'s Comprehensive Test Ban Treaty Organization, cited readings from a California-based measuring station of the group.

Initial readings are "about a billion times beneath levels that would be health threatening," the diplomat told The Associated Press, speaking on condition of anonymity because the CTBTO does not make its findings public.

APNewsBreak: Source: minuscule fallout reaches US