Authorities are trying to determine why three high-ranking county officials entered a sealed coalmine, resulting in their deaths from inhaling poison gas Saturday in Kaijiang, Southwest China's Sichuan Province.

Preliminary findings suggest the three died from inhaling carbon monoxide, but the reason why they entered the coalmine remains unknown.

On Saturday afternoon, Zhang Xiaotong, deputy director of Kaijiang Public Security Bureau, drove a police car to an illegal coalmine that had been sealed by the government, the Chengdu-based West China City Daily reported Monday.

The deputy director of the county's bureau of radio and television, surnamed Chen, and the bureau's former deputy director, surnamed Cui, were together with Zhang during the trip. The three officials were found dead in the coalmine Saturday night.

Concerns were raised when Zhang's colleagues were unable to reach him, as he had been scheduled to deliver a memorial speech at a funeral on the same day. Villagers living near the coalmine contacted the police and told them the three people might be trapped there.

The local government held an emergency meeting Sunday morning after a preliminary investigation.

"It was the officials' own decision to go into the sealed coalmine," an official from the county's publicity department told the Global Times Monday.

"There is no evidence to show this is a criminal case yet," said the official.

There had been speculation in Kaijiang that the three officials were surveying the coalmine to see if there was any possibility to re-exploit it, as coal prices had soared recently, the report said.