Twenty-five miners were killed and at least four were still unaccounted for today after an explosion in a mine in West Virginia - the worst US mining disaster for more than 25 years.

A police officer stands at the entrance to the mine owned by Massey Energy. (Photograph: Chris Keane/Reuters) The search for survivors of the explosion more than 300m (1,000 ft) underground at a remote plant with a history of safety problems was suspended because rising methane gas levels posed a high risk of another blast. Bore holes were being drilled to allow toxic gas to escape.

Officials hoped some of the miners had survived the initial blast at Massey Energy's Upper Big Branch mine at Montcoal yesterday afternoon and reached airtight chambers stocked with food, water and enough oxygen for four days.

However, rescue teams who made it to one of two shelters found it empty and gas levels prevented them reaching the second. State mining director Ron Wooten said rescuers had not given up hope and would try to reach the missing miners.

But Kevin Stricklin, an administrator for the federal Mine Safety and Health Administration, said the situation was "dire" even though rescuers trying to reach the trapped miners had found that some workers had taken emergency oxygen supplies from a cache in the mine.

Nick Rahall, who represents the district in the US House of Representatives, said: "West Virginians are tough, we will bind together."

The cause of the blast is unknown but safety officials said the mine had previous violations for not properly ventilating methane gas. Miners were leaving on a vehicle that took workers in and out of the long shaft when a crew ahead of them felt a blast of air and went back to investigate. They found nine workers, seven of whom were dead. Others were hurt or missing about a mile and a half inside the mine.

Miner Benny R Willingham, 62, was among those who died, according to his sister-in-law Sheila Prillaman. She said family members were angry because they learned of Willingham's death after reading it on a list Massey posted, instead of being contacted by the company.

Massey Energy is among the US's most profitable coal producers. In the last year, federal inspectors have fined the company more than $382,000 (£251,000) for violations involving ventilation and equipment at the plant which is run by a subsidiary, Performance Coal Co. Three other deaths have occurred at the mine in the last 12 years.

Last year, 34 US miners were killed on the job. The accident is the worst since 27 miners were killed at Emery Mining Corporation's mine in Orangeville, Utah, in 1984.

The US accident happened as authorities in China battled to find 33 missing miners in a flooded mine at Xiangning, where 115 workers trapped for more than a week have been rescued and five bodies have been found.