© AFP Photo
Bystanders remove an injured man beside a burning passenger bus after an explosion in Karachi on Dec 29, 2012
At least six people were killed when a loud explosion ripped apart a passenger bus parked outside the gates of Karachi Cantonment Station, the main railway station in the city.

The large blast completely ripped opened the roof of the bus, scheduled to depart for Sargodha, which caught fire following the explosion.

"There are reports of five people being killed in the blast. The injured have been shifted to Jinnah Hospital," said Ahmed Chinoy, the head of the Citizen Police Liaison Committee (CPLC).

At least 48 other people were also injured in the blast, with five of them said to be in critical condition, hospital officials said.

"We have received 48 patients, some of which are critical. Six people killed have been shifted to the mortuary," confirmed Seemi Jamali, a senior doctor at the Jinnah Hospital.

It was not immediately clear what had caused the blast, officials said, adding that a bomb disposal team was trying to determine whether it was caused by a bomb or an exploding compressed natural gas cylinder.

"So far, we are unable to say whether the explosion was a terrorist attack or a cylinder blast," said Chinoy.

Karachi's Cantt Station is one of the busiest areas of the city. It is one of the main terminals for inter-city travel as well as outside the city. The bus and coach terminals right outside the station are also used by hundreds everyday for travel to different parts of the country.

Police had cordoned off the area while an emergency was imposed at the Jinnah Hospital, which is located close to the blast site.