DANTE, VA., DEC. 29 -- High levels of carbon monoxide in a coal mine where a weekend explosion trapped a miner pointed to underground fires and officials said today they are considering sealing the mine.

The fate of miner Ted C. Street, 47, of Rowe, Va., is unknown, but officials said there was little possibility he survived the blast Saturday at Double R Coal Co.'s No. 2 mine in southern Dickenson County.

"We have to say that with the force of the explosion and the adverse conditions that developed over the last 72 hours, the chances are not good," said Mike Abbott, a spokesman for the mine division of the Virginia Department of Mines, Minerals and Energy.

He said from his Big Stone Gap office that sealing the mine had "certainly been discussed up there."

Excessive levels of explosive methane gas at the mine prevented rescue crews from reentering the shaft this afternoon.

"We are presently getting high readings of methane -- also high concentrations of carbon monoxide," Abbott said.

"We have to suspect that there could possibly be mine fires burning," he said.

A fan was being used to ventilate the mine. Rescue crews were ready to go back into the mine if the air became safe enough, but Abbott said use of the fan could be keeping underground fires alive.

The combination of mine fires and methane could lead to another explosion, Abbott said.

Early today, authorities tested the concentration of gas in the mine after drilling a 415-foot hole to the mine's deepest point so a sampling instrument could be lowered inside.

"We are presently taking samples and we're trying to see if we can pick up any kind of trend in terms of fluctuations or decreases in the amount" of the gases, Abbott said.

Rescue crews went 1,000 feet into the mine Sunday before they were brought out because of concern about the possibility of more explosions after methane readings of 6.6 percent were taken.

"Anything from 5 to 15 percent is explosive," said Frank O'Gorman, a U.S. Mine Safety and Health Administration spokesman. "But we try to keep levels under 1 percent."

The volatile methane occurs naturally around coal seams.

Gas levels recorded this morning were 29 percent to 30 percent, Abbott said, and they remained at that level into the afternoon. Today's readings differed substantially from earlier tests because Sunday's 6.6 percent reading was recorded at the ventilation fan and today's readings were taken from the most recently mined area, Abbott said.

The cause of Saturday's explosion is a mystery that cannot be solved until officials can enter the mine and inspect the area where the explosion occurred, Abbott said.