The Observatory says radioactive material from Fukushima nuclear plant is unlikely to reach Hong Kong.
Predicting the probable trajectory of spewed materials from the damaged plant more than 3,000 kilometres from Hong Kong, the weather scientists said the city would be under the influence of a westerly air flow from China until Friday.
'All the radioactive materials in Fukushima will be blown east towards the Pacific Ocean by the westerly and they will not reach Hong Kong,' said Leung Wing-mo, assistant director of the Observatory in charge of radiation monitoring.
Edmund Leung Kwong-ho, chairman of the city's Energy Advisory Committee, said any pollutants that travelled far would be greatly diluted during the journey.
'Substances billowing out from a stack will normally have their concentration diluted by 30,000 times for every 5km they travel,' he told government officials.
But Leung also said it was possible that radioactive pollutants might be present in rain.