A wall in a coal mining pit collapsed in the central Philippines, killing three workers and leaving at least six others missing, a provincial governor said Friday.

Antique provincial Gov. Rhodora Cadiao said she ordered the operator to stop work at the open Panian pit on Semirara Island until the missing workers have been found.

"They promised me they'll stop their mining operations in that area until they have recovered all the missing," Cadiao said by telephone, adding she deployed a Semirara town emergency-response team to the accident site to get more details.

Investigators haven't yet determined what caused the collapse.

A similar accident in 2013 in Semirara in Antique, about 350 kilometers (215 miles) south of Manila, killed at least 5 workers.

Coal makes up for about a third of energy supply in the Philippines.