Japan's nuclear regulator expressed growing alarm yesterday at increased contamination beside the seafront of the stricken Fukushima Daiichi nuclear power station and urged the plant's operators to take protective measures.

Fukushima's operator, Tokyo Electric Power, has acknowledged problems are mounting at the plant north of Tokyo, the site of the world's worst atomic disaster since Chernobyl in 1986.

The company said radiation levels in groundwater had soared, suggesting highly toxic materials from the plant were getting closer to the Pacific more than two years after three meltdowns triggered by a massive earthquake and tsunami.

Shunichi Tanaka, head of the new Nuclear Regulation Authority, told reporters he believed contamination of the sea had been continuing since the March 2011 catastrophe.

The NRA "strongly suspected" radiation was contaminating the Pacific, Kyodo news agency said in an earlier report from a weekly NRA commission meeting, citing Mr Tanaka.