The blast, on the eve of ceremonies to mark the troubled island nation's 60th anniversary, came hours after a crude bomb went off in a zoo in the capital and wounded four visitors.

Both attacks were blamed by the government on the Liberation Tigers of Tamil Eelam fighting for an independent homeland for minority Tamils in the north and east of the island.

"When I entered the station after buying a ticket I heard a loud explosion. I ran off with the others," said witness S.Ilangovan after the blast at the crowded Fort station in central Colombo.

Fighting between the Sri Lankan military and the LTTE rebels has escalated since the government scrapped a six-year ceasefire last month, saying the rebels were using it to rebuild and re-arm.

Local television showed footage of bodies lying on the railway station platform in a pool of blood. Four compartments of a train at the island's main railway station were badly damaged. Shattered glass and shrapnel were scattered around.