Oleg Goloskokov, a spokesman for the station, said contamination caused by a spillage of radioactive dust had been cleaned up. There was no threat to the environment.
The leak occurred when staff changing filters used to pump air from inside the "sarcophagus" encasing the ruined fourth reactor left the old filters in a room by the third reactor.
The incident detracted from commemorations of the 10th anniversary of the disaster which began earlier today with a candlelight procession through Slavutych, the new town created 20 miles from the plant. The parade at 1.24am marked the moment when staff lost control of the reactor.
Monuments to the 350,000 "liquidators" who fought the blaze at the station were unveiled throughout the country.
In neighbouring Belarus, which received 70 per cent of the fall-out, mourners were to stage a march through the capital Minsk. Nationalists opposed to President Alexander Lukashenko's pro-Russian policies planned a rally of their own.
Nearly half of the respondents in a poll in Moscow said a similar catastrophe could happen in Russia. Of 1,037 residents polled 45.5 per cent said it could happen again.