MOSCOW (Reuters) - An explosion at a weapons disposal site in central Russia on Tuesday blew windows shut in a city 30 kilometers away but preliminary reports indicated no one was hurt, according to the government and witnesses.

Some 4,000 tonnes of ammunition accidentally detonated as it was being unloaded by soldiers at the site, near the city of Orenbourg, Russia's Investigative Committee said in a statement, adding that it was investigating possible negligence.

There were no casualties, according to preliminary information, the Ministry of Emergencies said. Authorities evacuated three villages and declared a state of emergency, the ministry said.

Television footage taken from the centre of Orenbourg showed a white mushroom cloud billowing from the site some 30 kilometers away. Witnesses said the blast had blown shut windows in the industrial city, which is about 1,500 kilometers east of Moscow.

Explosions at sites to store or dispose of ammunition have plagued the Russian army, accused by critics of negligence or lax compliance with regulations more than 20 years after the fall of the Soviet Union. An explosion at an ammunition disposal site in central Russia killed six soldiers and injured four on May 2.

(Reporting by Gleb Bryanski; editing by Jason Webb)