By Juliet Hindell in Tokyo

Executives in charge of a nuclear reactor in Japan where 50 tonnes of radioactive water accidentally leaked earlier this week say radiation from the leak was 11,500 times the safety limit.

The earlier figure given was 250 times the limit, and the change has sparked accusations of a cover-up.

The cooling water leaked from a pipe in the building that houses the reactor at the Tsuruga nuclear power plant in northern Japan earlier this week.

It took Japan Atomic Power, the company that operates the plant, 14 hours to shut down operations after the leak was discovered.

But the company insisted that the surrounding environment was not in danger of radioactive contamination because the leak was contained within the reactor.

No one was injured in the accident, which was classified as a one on an international scale that starts at zero and goes to seven.

The huge gap between the two figures given by Japan Atomic Power has prompted accusations of a cover-up.

Anti-nuclear campaigners say the company is trying to play down the accident by announcing a low estimate.

A series of incidents at Japanese nuclear power stations in recent years have undermined confidence in the safety of this form of energy production.

Misleading, or at least badly presented figures like this are unlikely to reduce that anxiety.