Inmates apparently set two fires during a riot over conditions inside Georgetown Prison, said Public Security Minister Khemraj Ramjattan. Those killed were inside the most secure section of the facility, he said.
The first fire was set late Wednesday and extinguished with no injuries reported. The second fire was set Thursday around noon and led to the fatalities, officials said.
Ambulances were seen entering the main gate of the facility, and officials said at least eight prisoners had been hospitalised.
The colonial-era prison holds about 1,000 prisoners even though it was built to hold less than 500 inmates. Police believe the inmates were protesting overcrowding and delays for prisoners awaiting trial.