Pandemic-related unrest has been growing in Sri Lanka's overcrowded prisons. Inmates have staged protests in recent weeks at several prisons as the number of coronavirus cases surges in the facilities.

Police spokesman Ajith Rohana said inmates created "unrest" on Sunday at Mahara prison, about 15 kilometres north of Colombo, and officials attempted to control the situation.

But "the unrest situation turned into a prison riot", he said on Monday, adding that prisoners tried to take control of the prison and hundreds attempted to escape.

The inmates "reportedly destroyed most of the property including offices inside the prison", Rohana said.

The guards opened fire, and the clash left six inmates dead and 35 injured, he said. Two prison officers were critically injured.

He said hundreds of additional police were deployed to help the guards and strengthen security around the prison.

An inmate was killed in similar unrest at another prison last week. Another died in March.

More than a thousand inmates in five prisons have tested positive for the coronavirus and at least two have died. About 50 prison guards have also tested positive.

Sri Lankan prisons are highly congested with more than 26,000 inmates crowded into facilities with a capacity of 10,000.

Senaka Perera, a lawyer with the Committee for Protecting Rights of Prisoners, said the inmates had been frustrated because their pleas for coronavirus testing and the separation of infected prisoners had been ignored by officials for more than a month.

Sri Lanka has experienced an upsurge in the disease since last month when two clusters - one centred at a garment factory and other at a fish market - emerged in Colombo and its suburbs.

Confirmed cases from the two clusters have reached 19,449. Sri Lanka has reported a total number of 22,988 coronavirus cases, including 109 fatalities.

Australian Associated Press