Irvine says the man killed by the blast had been working to remove snow from a tennis court heated by propane.

GRANTHAM, N.H. (AP) -- An explosion collapsed an elevated tennis court Sunday, killing one person and injuring three others at a private recreational community, authorities said.

The four men were removing snow from the court when the blast tossed them into the air, then buried them in rubble and snow.

Scott Irvine, a doctor who lives near the court, said one of the men was found buried in snow nearly 20 feet away. Irvine said he performed CPR but could not revive the man.

Two people were blown over a 12-foot-high fence, said Fire Chief Bob Seavey.

Irvine said one man was treated at the scene, another was flown a hospital with critical injuries and a third suffered broken bones. He said he believed three of the men were in their 70s and one in his mid-60s.

Seavey said investigators don't know what caused the blast, but Irvine said, "one man said they hit something with the snowblower and heard a loud boom." He said a stream of fire was coming from a gas pipe when he arrived at the scene.

The aluminum platform, which had sat about four feet off the ground, was covered with about 20 inches of snow from a storm Friday night.

The recreational community in Grantham, about 50 miles northwest of Concord, has a golf course, 13 tennis courts and hiking and ski trails.