At least 25 workers have been killed after a section of a coal mine in the US state of West Virginia collapsed following an explosion.
Officials on Tuesday said that four others were still trapped more than a 1,000 feet underground at Massey Energy Company's Upper Big Branch mine in Montcoal, Raleigh County.
Earlier, Kevin Stricklin, an administrator for the federal mine safety and health administration, said officials hoped some of the missing had survived the initial blast and were able to reach airtight chambers stocked with food, water and enough oxygen for them to live for four days.
However, rescue teams who made it to one of two nearby shelters, said it was empty, and the gas levels prevented them from reaching the second one.
"It does not appear that any of the individuals made it to a rescue chamber," Stricklin said at a news conference on Tuesday.
"The situation is dire."
John Terrett, Al Jazeera's correspondent reporting from the site, said all rescue work had been suspended until bore holes could be drilled to allow for toxic gases to be ventilated from the mine.
"Joe Manchin, the governor of West Virginia, confirmed that 25 miners were killed in the explosion," Terrett said.
"Seven of them have been positively identified and removed from the mine, but there are still 18 bodies inside."
Terrett said the govenor described the build up of methane gas and the huge explosion as the worst mining disaster in US history for the last 40 years.
"The explosion tore the roof off the mine shaft and damaged all communications in and around the neck of the mine shaft as the miners were coming out," Terrett said.
A total of 29 miners were in the area when the blast happened on Monday night.
Spotty safety record
The operation about 50km south of Charleston, has a history of violations for not properly ventilating highly combustible methane gas, safety officials said.
Federal records show three miners have died on the job at Upper Big Branch mine, operated by Massey subsidiary Performance Coal, since 1998.
Massey ranks among the top five coal producers in the US and is among the industry's most profitable, but it has a spotty safety record.
The federal mine safety administration fined Massey a then-record $1.5m for 25 violations that inspectors concluded contributed to the deaths of two miners trapped in a fire in January 2006.
The company later settled a lawsuit naming it, several subsidiaries and Blankenship as defendants.
Subsidiary Aracoma Coal later paid $2.5m in fines after the company pleaded guilty to 10 criminal charges in the fire.
Last year, the number of miners killed on the job in the US fell for a second straight year to 34, the fewest since officials began keeping records nearly a century ago.
That was down from the previous low of 52 in 2008.