Difficulty in finding cause of damaged reactor smoke

Efforts have resumed at Japan's Fukushima Daiichi nuclear power plant to restore electrical power and cool its overheating reactors, seriously damaged by the 11 March earthquake.

Work was interrupted for the second time in 24 hours after steam and smoke was emitted from two of the reactors.

Japan's Chief Cabinet Secretary Yukio Edano told a press conference it has been extremely difficult to see inside the damaged reactors to establish the cause of the vapour.