HEFEI - Five people harvesting ginger in east China's Anhui Province were killed on Friday when heavy rain caused a rotten patch of the root to emit poisonous carbon monoxide, local authorities suspect.

A couple in Dafeng Village of Qimen County were found unconscious on Friday morning in a pit used for storing ginger after they went missing on Thursday after leaving their home for ginger harvesting, said a spokesman with the county government.

Three villagers who tried to pull them out also fell unconscious in the pit before others called the police.

The five were lifted out of the pit, but died at the scene despite medical efforts.

Their deaths followed days of heavy rain. The dampening of the rotten ginger may have caused it to emit deadly carbon monoxide, police say. Further investigation is under way.

Chen Liang, a doctor of biochemistry with the University of Science and Technology of China, said rotten plants can release carbon monoxide, which may lead to poisoning and even death in human beings. Another possible reason for their deaths is that plants could have consumed much of the oxygen in the cellar-like pit, potentially leaving people to suffocate once they had entered it, according to Chen.