A passenger bus after it exploded in Karachi on December 29, 2012
An explosion on a bus in Pakistan's largest city Karachi Saturday left at least five people dead and wounded 35 others, police said.
It was not immediately clear what had caused the blast in Sadar, a congested shopping area of Karachi, 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.
"At least five people were killed and 35 others were wounded," police surgeon Jalil Qadir told AFP.
Karachi is in the grip of a long-running wave of militancy, political and sectarian violence.
Pakistan says 35,000 people have been killed as a result of terrorism since the 9/11 attacks and the 2001 US-led invasion of neighbouring Afghanistan.