MONTCOAL, W.Va. — Rescuers this morning drilled a first hole into a coal mine where 25 people died in an explosion but got no response from possible survivors when they banged on the drill pipe to send a signal.

Three more vents needed to be bored to release poison gases before searchers could look for four people still missing in the worst U.S. mining accident in more than two decades.

Gov. Joe Manchin said the first hole reached the Upper Big Branch Mine after boring through about 1,090 feet of earth and rock. Rescuers banged on the drill pipe for 15 minutes in hopes of being heard below ground.

"We did not get any response back," Manchin said at an early morning briefing. Officials said they also plan to set off three small explosions on the surface to send a seismic signal to the mine.

Miners are trained to bang back on the drill's casing, Manchin said, and to respond similarly to the surface charges. Sections of mine roof contain numerous metal bolts that help keep it in place and that trapped miners can bang on to signal their presence.

The company that runs the mine, Massey Energy, frequently sidesteps hefty fines by aggressively contesting safety violations, including recent problems with the ventilation system that clears away combustible methane gas.

By The Associated Press