A bomb tore through an elite club in the Colombian capital of Bogota, killing more than 20 people, wounding 100 and raising fears that a militant left-wing group is making good its threats to attack the ruling class.

The powerful bomb rocked the 10-storey El Nogal Club in north Bogota early today, blowing brick and mortar on to a busy road, collapsing floors, and starting a fire that burned for about two hours through much of the building.

No one claimed responsibility for the attack, but the Revolutionary Armed Forces of Colombia, or FARC, said several months ago that it intended to attack Colombia's elite. The rebels have recently brought their four-decade war from the countryside into the cities.

The club was one of Colombia's most exclusive, and a symbol of wealth and power. It was frequented by politicians and business executives and included restaurants, a mini-golf course, a gym and rooms for overnight guests.

Witnesses said children were to put on a ballet show at the club last night, and several children were among the injured. Their fate was not immediately known.

Jorge Velandia, who works at the miniature golf course, said the blast opened a hole in one of the floors and people tumbled through.

"It was a huge explosion. I thought an airplane had crashed outside," said Luis Moreno, who lives across the street from the club on Seventh Avenue and whose apartment building's windows were shattered.

Bogota Mayor Antanas Mockus said more than 20 people were killed and 100 or more injured in the blast caused by a 450lb bomb.

It was the worst terrorist attack in Colombia since Pablo Escobar's Medellin drug cartel orchestrated a wave of bombings and assassinations in the 1980s and early 1990s in Colombia's cities to avoid his extradition to the United States.

After Escobar was killed by police in 1993, Colombia's cities saw little of the violence frequently seen in the countryside.

After today's bombing, black smoke poured from the building and flames licked out from upper windows. Scores of people stumbled from the wrecked building, many of their faces streaked with blood.

President Alvaro Uribe, who has promised to crack down on the 40-year insurgency, visited the scene at midnight with his top security officials.

The attack was the second blow to hit Colombia in as many days.

On Thursday, a small plane carrying Minister of Social Welfare Juan Luis Londono and four other people disappeared on a domestic flight. Suspected rebels fired at a helicopter searching the for the plane in Andean mountains of central Colombia, an area controlled by FARC rebels

The helicopter was hit four times but returned safely to its base and no one was injured.