MANILA, Philippines -- The deadly blast at the Glorietta 2 in Makati City originated from the basement, the Philippine Bomb Data Center said Saturday.

And while Chief Inspector Reynold Rosero said the explosion originated underground, authorities are still clueless on what kind of explosive caused the blast, which killed at least nine people and injured over a hundred others on Friday afternoon.

"The explosion came from the underground that's why there was a crater-like structure in the stairs going to the basement," Rosero told reporters.

Alfonso Reyes, spokesman of the Ayala Land Incorporated who operates the mall said the basement was under the delivery bay of a grocery shop. The public has limited access to the area.

Rosero said that although chemical analysis showed RDX was present in the samples gathered from the blast site, it was still possible that other chemicals caused the blast.

"We are looking at all angles..especially (as) there is sewage grease in the area and there's also a possibility that methane gas caused the explosion," he said.

Rosero added that the post-blast investigation might take more days as the blast site is knee-deep flooded with water from the sprinklers and as its ceiling is on the verge of collapsing.