COLOMBO, May 11 (Xinhua) -- Over 20 were killed and some others injured as a bus plunged off a cliff in Kotmale in Sri Lanka's Central Province on Sunday morning, police said. 

The injured were under close medical supervision in a hospital. 

The Sri Lanka Transport Board sent a team to the scene to investigate the accident. 

Police said that they were also investigating the accident. 

Road accidents are frequent in Sri Lanka. A total of 592 Sri Lankans have died in 565 fatal road accidents as of April 2 this year.