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TALLMANSVILLE, West Virginia (CNN) -- High levels of toxic carbon monoxide in a coal mine where 13 miners are trapped Tuesday have officials discouraged in their quest to rescue the men.

But hope remains.

"They could be in another location or they could be barricaded somewhere," said Ben Hatfield, president of International Coal Group, which owns the Sago Mine in Tallmansville, West Virginia.

"This carbon monoxide level far exceeds regulatory limits for respirable air." Hatfield said. "Therefore we are very discouraged by the results of this test."

The miners were trapped early Monday after an explosion and are believed to be about 260 feet below the surface at the end of an angled shaft about 2 miles long. (Watch what officials said about the level of poisonous gas -- 2:09)

Hatfield also said rescuers on the surface pounded on a drill that was placed in an area where the miners were thought to be at the time of the blast. There was no response.

There has been no contact with the miners since Monday's blast.

Views from a camera dropped through the drill hole were inconclusive, Hatfield said.

"No barricades or survivors were seen, but there was also no evidence of substantial explosion damage to the installed equipment that was in view," Hatfield said.

"We remain determined to continue the search so long as there is hope, and hope remains," he said.

Rescuers were sending a track-mounted robot into the main mine shaft. The robot has reached 9,200 feet and can probe another 3,500 feet into the mine. (Interactive: Long path to accident site)

"At this point, our effort is focused on the robotic search," Hatfield said. The cause of Monday's explosion was still unknown, he said.

Near the mine, the mood of hundreds of family members gathered Tuesday morning at the Sago Baptist Church changed considerably after officials briefed them. (Watch where relatives are waiting and weeping -- 1:05)

They're despondent, but holding on to hope, said a friend of one of the miners. Terri Goff, a relative of one of the miners, described his reaction after the briefing.

"We got outside and cried a little bit and we realized that there's still hope," he said. "They could be stuck in another place and ... we can still find these guys, and we need to."

The absence of miners near the area of the concentrated carbon monoxide offered relatives hope that their loved ones escaped to another part of the mine.

The explosion went off in the Sago Mine about 6:30 a.m., and six miners from another team managed to escape the explosion unharmed, authorities said.

The mine is about 8 miles south of the town of Buckhannon in Upshur County near Tallmansville. (Map)

Gov. Joe Manchin said the drilling equipment being used is the same equipment used in the July 2002 rescue of nine miners in Somerset, Pennsylvania. Those miners were pulled to safety after being trapped for 77 hours in a flooded mine.

The cause of Monday's explosion was not immediately known. Manchin said there were high levels of carbon monoxide shortly after the explosion, but those levels have since subsided to a level safe enough to send rescuers in.

The trapped miners are believed to be about 10,000 feet inside the shaft. Shortly after the blast, a mining supervisor and other workers made it about 9,000 feet before turning back due to poor air quality, officials said.

Officials are hoping the experience of the miners pays off. Some of the trapped miners have 30 to 35 years of experience, and all have been working for at least several years.

"It is an experienced crew," said Gene Kitts, the company's senior vice president. "We're just praying that they've had the opportunity to put their training to use."

Kitts said that when an accident happens, a miner is taught to go to "the safest area he can find, barricade himself and wait for someone to come."

"That's what we're hoping is the situation here," he said.

The miners were equipped with about one hour of breathable oxygen.