At least 25 people have been killed – four of them guards – and more than 100 injured in prison riots in western Sri Lanka.

The two days of violence at Negombo Prison, in a coastal town north of Colombo, began with clashes between two groups of inmates.

Prisoners are alleged to have grabbed prison guns on Sunday. Two people were killed that day, with dozens injured. Later, groups of male prisoners, and women from an adjoining unit, climbed on to prison rooftops demanding to be released.

Fresh violence erupted on Monday when inmates tried to rush the prison gates. Security forces were deployed and multiple gunshots heard from inside the prison.

The violence was reportedly triggered by a clash over an inmate informing on a drug trafficking operation inside.

Some of the wounded were taken to Negombo Hospital. The hospital director told the AFP news agency that some had bullet wounds, while others had sustained cuts and severe bruises. Others were transported to Colombo National Hospital.

Police said part of the prison’s roof collapsed during the incident, which injured some of the women involved, AFP reported.

Crowds of inmates’ relatives gathered outside on Monday as the situation unfolded. Some told BBC Sinhala they had not been given information about where their relatives were, or who was alive and who had died.