Christchurch's AMI stadium could be capable of hosting Rugby World Cup matches, Prime Minister John Key said today as the Government studied reports on damage caused by the February 22 earthquake.

John Key should just tell people the truth about what he knows of Christchurch's chances of hosting the RWC, says opposition leader Phil Goff.

A secret report into the state of Christchurch's AMI Stadium reportedly reveals it won't be able to host RWC games, a British news website says.

The Japan quake was 8000 times stronger than Christchurch's and unzipped a faultline half the size of the North Island, a NZ scientist says.

Christchurch Mayor Bob Parker says the thoughts of his quake-stricken city are with Japan following Friday's magnitude 9.0 earthquake which devastated much of the country and left thousands dead.

Japanese officials have confirmed a second hydrogen explosion has occurred at the Fukushima Daiichi nuclear power plant, while a warning of a second tsunami has been cancelled.

More than half a million people have been forced from their homes in quake and tsunami-hit northern Japan, petrol has run dry and supermarkets are empty in what its prime minister says is the worst crisis to hit Japan since WWII.

Japanese officials warned of a possible second explosion at a nuclear plant crippled by the earthquake and tsunami as they raced to stave off multiple reactor meltdowns, but they provided few details about whether they were making progress.

Three nuclear power plants in Japan have suffered failure, with a top Government official warning a meltdown at one of the plants was "highly possible". Over 10,000 people are thought to be missing as officials fight to avoid a catastrope

The family of a NZ man in Japan have heard nothing from him since hours before the deadly quake and tsunmai which struck on Friday night