SINGAPORE: Singapore on Monday said it was testing food imported from Japan for radiation as another explosion rocked an earthquake-hit atomic plant and raised fears of a radioactive catastrophe.

"As a precautionary measure, AVA (the Agri-Food and Veterinary Authority of Singapore) will monitor Japanese produce based on source and potential risk of contamination," the food regulator said in a statement.

"Samples will be taken for testing for radiation. Fresh produce will have priority. AVA will continue to closely monitor the situation and its developments."

The AVA said the bulk of Japanese imports arrive by sea, but high-end Japanese restaurants in Singapore routinely use air freight to fly in produce such as raw fish -- integral to sushi and sashimi -- to ensure its freshness and quality.

The city-state has a large concentration of restaurants serving Japanese cuisine, which is very popular among Singaporeans.

Government figures showed the city-state's imports from Japan totalling Sg$33.3 billion ($26.2 billion) last year.

An explosion was seen on Monday at the ageing Fukushima No. 1 atomic plant 250 kilometres (160 miles) northeast of Tokyo, after an earlier blast on Saturday.

The plant's operator TEPCO said that nine people were injured in the blast in what authorities said was probably a hydrogen explosion which apparently did not damage the reactor.

The power station was hit in an 8.9 magnitude quake on Friday that spawned a huge tsunami which smashed into Japan's northeast coast.

Saturday's explosion released radioactive vapours into the surrounding area, but the Japanese government said radiation levels released at that time were not high enough to affect human health.