Two huge earthquakes and a series of powerful aftershocks ripped through central Japan yesterday, causing a radioactive leak at a nuclear power station and leaving more than 20,000 homes without water or electricity.

They brought unexpected chaos to the first weekend of campaigning for critical Upper House elections on July 29 – an already messy battle that has become a referendum on Shinzo Abe, the Prime Minister, and the 52-year rule of his Liberal Democratic Party (LDP).

Hundreds of houses in the mainly rural prefecture of Niigata caved in as the first tremor, registering 6.8 on the Richter scale, turned walls to powder. Seven people were reported killed and at least 800 injured, mainly by objects hurled around by the shaking. Hours later a second earthquake, registering 6.6, struck the Sea of Japan.

Rescue and other aid efforts were helped by members of Japan’s Self Defence Forces – producing the unfamiliar sight of military vehicles filled with uniformed men rumbling through small rural towns.

Officials at the Kashiwazaki nuclear plant said that a small amount of water containing radioactive substances leaked into the sea after the first tremor struck, but they said: “The leakage is believed to be far below the levels that could affect the environment.” The tremor also started a fire at the plant.

The earthquakes, which caused landslides across Niigata, were the second natural disaster to hit Japan this Bank Holiday weekend. On Friday and Saturday a “super-typhoon” blew 250km/h (150mph) winds along the eastern coast, killing four people and leaving a trail of wreckage in its path.

The Prime Minister had already run into intense political turbulence. With his cabinet embroiled in scandal after scandal and his political agenda hijacked by a pensions fiasco, the preweekend polls had swung heavily against all the LDP candidates. Some ruling party members defending their Upper House seats have even questioned privately whether Mr Abe is an asset to their campaign or a liability.

Despite the natural violence unleashed on Japan since Friday and the seemingly unstoppable political head-wind, analysts said that Mr Abe had emerged from the national holiday in a stronger position.

The earthquakes gave him a chance to play the one trump card he has not yet had the chance to use – his relative youth. The youngest postwar Japanese Prime Minister, stumping on behalf of the local LDP candidate in the district of Nagasaki, dramatically cut short his engagement and ran towards his motorcade.

A helicopter whisked him to Tokyo, where he changed into the blue overalls, boots and baseball cap of Japanese emergency teams. After a rushed public appearance, where he promised to “make the utmost effort to wipe away the anxiety of the victims of the disaster”, he took off in another helicopter and headed for Niigata.

His exit from Nagasaki was far more statesmanlike and dynamic than seemed possible an hour before his speech. The city is still smarting from a supposed gaffe by his former defence minister over its atomic bombing. Mr Abe’s appearance there, analysts said, was only ever an optimistic bid for clemency. In Niigata, too, the earthquake gave Mr Abe an opportunity to show his leadership in a key district likely to turn against him.

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