The massive blast was heard across the city.
The car of Sri Lanka's sports minister, Gamini Lokuge, was also caught up in the blast, police said. He escaped unhurt, but his driver was among the dead.
At least 62 civilians, 30 policemen and three soldiers were among those injured, said national hospital director Hector Weerasinghe.
"A motorbike carrying an LTTE (Liberation Tigers of Tamil Eelam) suicide bomber rammed into a bus carrying police personnel," Nanayakkara said.
The attack occurred outside a Buddhist temple in the Fort area of Colombo's commercial district, a high security zone surrounded by several rings of military and police check posts.
The area is home to the official residence of the island's hawkish President Mahinda Rajapakse, the five-star Hilton and Galadari Hotels and the t