Local radio reports said that among the victims were two police officers and a nine-year-old child.

Officials said the explosives had been placed on a motorbike and detonated by remote control.

Police have blamed left-wing rebels for the attack, which took place at 0300 (1000 GMT) as revellers were leaving bars and nightclubs in a busy district.

General Luis Alberto Ardilla, an army commander in the city, said the bomb was probably the work of the Revolutionary Armed Forces of Colombia (FARC), the country's largest rebel group.

The motorcycle was strategically placed outside a packed nightclub to cause the greatest number of victims, he said.

"People were leaving to go home when the motorcycle exploded," he said.

Earlier this month, at least eight people were killed when a bomb strapped to a horse exploded in a market in the town of Chita, north-east of the capital, Bogota.

That attack was also blamed on the FARC.

Leftist guerrillas, right-wing paramilitaries and the government have been fighting each other for four decades in Colombia.

In the past decade alone, more than 35,000 people are believed to have been killed in the fighting.