"We think it was dynamite," a local official in the southern city of Taiz where the blast took place told Reuters. Al Jazeera had earlier reported the blast took place in a fireworks warehouse.

The official said the pre-dawn explosion caused the collapse of a three-story building with six residential apartments, and partly destroyed two adjacent homes. At least nine bodies were pulled from the rubble and rescue workers were looking for 10 more believed buried.

Some 15 people also were injured in the blast but survived.

The official said the dynamite was believed to have belonged to a Yemeni businessman and contractor who used explosives in roadbuilding works to flatten hills, but who did not live in the building.

An investigation into the cause of the blast was continuing, but based on initial findings there was no indication it was anything other than an accident, the official said.

Yemen rose to the forefront of Western security concerns after the Yemeni arm of Al-Qaeda claimed responsibility for a failed attempt to bomb a US-bound plane in December.

Western governments and neighboring Saudi Arabia, the world's biggest oil exporter, fear Yemen could become a failed state in which Al-Qaeda could exploit instability to recruit and train militants to launch attacks in the region and beyond.

In addition to fighting Al-Qaeda, Yemen is also trying to bring an end to a northern Shiite rebellion while also facing simmering separatist sentiment in the south, where tensions have escalated in recent weeks.