Hong Kong, March 30 (DPA) Radioactive dust believed to be from a crippled nuclear power plant in Japan has been detected nearly 3,000 kilometres away in Hong Kong, officials said Wednesday.

The amounts detected were so miniscule it would take up to 2,500 years of continued exposure to have any perceptible effect on human health, an official from the Hong Kong Observatory said.

The radioactive dust, believed to have blown in on a westerly wind, was the first detected in Hong Kong since the March 11 earthquake and tsunami, which damaged the plant in Fukushima and matches similar readings on the east coast of China in recent days.

"It would take 800 to 2,500 years of continued exposure to the detected levels in order to receive the radiation dosage equal to one X-ray," a government spokesman said.

Hong Kong's 600 Japanese restaurants have lost an estimated 20 percent of business since the March 11 disaster because of fears over radiation contamination, the South China Morning Post said Wednesday.