One man lost part of his leg and four other people were injured by flying debris as they watched the planned implosion of an abandoned power plant in Bakersfield, California, early on Saturday morning, officials said.
The 43-year-old "suffered a traumatic partial amputation of one leg and major injuries to the other," the Bakersfield Police Department said in a statement.
Shrapnel from the blast also hit four other spectators, causing minor injuries, said Kern County Fire Department fire engineer Leland Davis, adding there were at least 1,000 onlookers.
Police said only two other spectators were injured and had not revised their tally.
One officer along the east perimeter heard screams for help at the 6 a.m. implosion, said police, who were on scene helping to control traffic and crowds.
The boiler facility, which belonged to Pacific Gas and Electric Company and was decommissioned in 1986, had two towers 140 feet tall and four 200,000-gallon (757 ,082-liter) empty water tanks, company spokesman Denny Boyles said.
It was being removed so the property could be cleared for sale under an agreement with the city of Bakersfield, he said.
Demolition subcontractors worked with police to establish a 1,000-foot (305-meter) perimeter beyond which a crowd had gathered to observe the demolition, Boyles said. He said the injured people were apparently outside the perimeter.
"Our thoughts and prayers are with those who were injured during the demolition," Boyles said, adding that the company and subcontractors are cooperating with local authorities investigating what went wrong.
The man with the leg injuries was taken to a local hospital and then to Fresno, California, for further treatment, police said. The four others who were injured received treatment at the scene, Davis said.