Parts of a British prison caught fire after inmates went on a riot there Saturday, and it took police hours to regain control of the lockup, an official said.
No casualties were immediately reported.
The blazes were lit inside the overcrowded Ashwell prison near Oakham, 100 miles north of London, after hundreds of inmates ran amok there, breaking into its shop area and raiding its pharmacy, police said.
Pete Chapple, leader of the Prisoner Officers' Association, said the riot ended Saturday evening.
"We anticipated it would go on throughout the night, but it has climaxed earlier than we thought," Chapple said. "It will take a long time to clear up the mess though, around 75 percent of the jail is damaged."
Britain's prisons are overcrowded, and opposition politicians have criticized the government for what they say is a failure to provide enough lockups.
Another union official, Glyn Travis, echoed those criticisms Saturday, saying that Britain's prisons were "bursting at the seams" while the staff totals were being cut, making riots inevitable.
Despite emergency measures such as early release programs, the U.K. is struggling to find space for the nearly 83,000 people it has in custody, 11 percent more than its national capacity.