All other people at the site have been accounted for, said George Zugel, director of safety and health for Frontier-Kemper Constructors Inc., which is building the 550-foot vertical ventilation shaft at the Gibson County Coal mine in southern Indiana.
Crews were working to remove the bodies after the late-morning accident, Sgt. Jay Riley said.
The "sinking bucket" can hold six to 10 people and is about 6 feet high, worker John Ervin said. Authorities did not say whether anyone other than the three victims was in the bucket.
"I don't understand how this could have happened," Ervin said.
At the start of a shift, the bucket typically takes about six people down to the work area at the bottom of the shaft, Ervin said. The bucket is inspected daily, he said.
The accident comes four days after six miners were trapped after a coal mine collapsed in Utah. Rescue teams were still trying to reach them on Friday.
Sen. Edward Kennedy, D-Mass., chairman of the Senate Health, Education, Labor and Pensions Committee said more attention needs to be paid to mine safety.
"These are terrible tragedies, not only for the workers and their families, but for all of the brave men and women who go to work each day in America's mines," said Sen. Kennedy, in a written statement.
He added, "As we move forward, we will be conducting a thorough investigation into the causes of both of these accidents, and the adequacy of our accident prevention and response efforts for all of our mines. Year after year, there have been too many lives lost and too many unanswered questions — we owe it to these workers and their families to find out exactly what happened, and how future disasters like these can be prevented."
The victims' names were being withheld until their families were notified, Zugel said. A message left at the Gibson County coroner's office was not returned.
The mine, owned by Tulsa, Okla.-based Alliance Resource Partners, is about 30 miles north of Evansville.
Officials from the Indiana Department of Labor and the Indiana Bureau of Mines are investigating at the mine, said Labor Department spokesman Sean Keefer.
The mine began production in July 2000. The last fatality was in November 2001, according to the U.S. Mine Safety and Health Administration. The miner died after being pinned by equipment, and operator error was cited as the cause.
In 2006, the company produced more than 3.5 million tons of coal, ranking second among the state's coal producers, according to the Indiana Coal Council.