The authorities in Guyana say at least 16 inmates have died in a fire inside a prison in the capital Georgetown.
Public Security Minister Khemraj Ramjattan said inmates had set fire to their mattresses to protest against conditions inside Camp Street prison.
He said they were protesting about overcrowding and delays for prisoners awaiting trial.
Mr Ramjattan said the protest had begun after a raid by police officers on cells looking for contraband.
Ambulances have been taking injured prisoners to hospital and hundreds of people came to the prison gates to find out about relatives inside.
On Wednesday there had been similar disturbances, with prisoners setting fire to their mattresses and repeating the act when the blazes were extinguished.
Camp Street Prison was built to accommodate 775 inmates but officials say it now houses more than 1,000.
Mr Ramjattan said a new facility at the prison would be completed to give the prisoners more room.
He said he was recommending some of them should be transferred to another prison.