Rescuers spread out to search a smoky labyrinth for two coal miners Friday after a conveyor belt caught fire deep underground in the second major mining accident in West Virginia in less than three weeks.

Close to a day after the fire broke out, safety crews had yet to make contact with the two men, said Doug Conaway, director of the state Office of Miners' Health Safety and Training. Their odds of survival "are a little bit long," Gov. Joe Manchin said.

It was unclear exactly where in the mine the men were. They were equipped with oxygen canisters that typically produce about an hour's worth of air.

The fire broke out Thursday night at the Alma No. 1 mine. Rescuers were hampered by heavy smoke that cut visibility to 2 to 3 feet. After the blaze was brought somewhat under control Friday, rescuers spread out to search four tunnels, each about four miles long. The mine extends as much as 900 feet below ground.

"I don't think we fully know the obstacles we're facing. How much smoke is there? What are the difficulties of traversing through there?" Conaway said.

David Roberts, co-manager of Refab Co., a mining machinery repair company, said a friend on the mine rescue team told him it was very hot -- up to 400 degrees -- and smoky inside the shafts.

Twenty-one miners were in the southwestern West Virginia mine on Thursday when a carbon monoxide monitor about 10,000 feet from the entrance set off an alarm. Nineteen of the miners escaped.

Jesse Cole of the federal Mine Safety and Health Administration said listening equipment would be set up to try to locate the missing men.

The governor was with the miners' families, who along with friends and co-workers gathered at the Brightstar Freewill Baptist Church to wait for news. Reporters were barred from the church.

Earlier this month, the governor joined another group of miners and relatives of those trapped after an explosion at the International Coal Group's Sago Mine, on the northern side of the state. Twelve miners died in the disaster. The sole survivor, Randal McCloy Jr., 26, remained hospitalized in a light coma Friday.

"Sago is very fresh in everybody's mind, but this is a different scenario," Manchin said. He said the families were hopeful, but he added, "They know that the odds are a little bit long."

Katharine W. Kenny, spokeswoman for Massey Energy, owner of mine operator Aracoma Coal, said the company was "very optimistic."

Air samples from a hole near the fire showed elevated levels of carbon monoxide, although not as severe as the levels at the Sago Mine. At one point, rescue teams were in the mine without breathing gear, Conaway said.

Robert Friend, acting deputy assistant secretary for MSHA, said there were some key differences between the Alma and Sago incidents.

The ventilation system continued to work at the Alma mine and no methane was detected coming out of the return, he said. That enabled rescuers to act more quickly.

The fire started where a side conveyor belt meets the main line that brings the coal out, authorities said.

Haskell Sheppard, 29, works the overnight shift as a repairman on the main conveyor belt. He said the line where the fire broke out had problems before, but nothing as serious as this. "Things are bound to tear up every once in a while," he said.

John Langton, MSHA's deputy administrator for coal mine safety and health, said belt fires can occur when belt rollers get stuck or out of alignment and rub against the structure supporting them. Another possible cause is the accumulation of coal or coal dust.

He said it's believed that the fire occurred on the belt drive, a big motor that powers the belt.

According to MSHA's Web site, the Alma mine received more than 90 citations from MSHA inspectors during 2005. The most recent were issued Dec. 20, when the mine was hit with seven violations for items such as its ventilation plan and its efforts to control coal dust and other combustible materials.

The mine was assessed $28,268 in penalties last year. It has not had a fatal accident since at least 1995, the earliest year for which records were kept. The mine had a better-than-average accident rate between 2001 and 2004, but last year 16 workers and one contractor were injured.