St. Louis ? Rapid-fire explosions and fire erupted at a St. Louis plant Friday afternoon, sending flames, debris and dense smoke hundreds of feet into the air.

The three-alarm blaze began around 3 p.m. at Praxair, a gas and tank company.

Susan Gore, a spokeswoman for Praxair, reported that all of the 70 workers at the plant were safe and had been accounted for.

Fire Chief Sherman George said when firefighters arrived at the scene, they determined that the building had been evacuated. He said firefighters waited until the explosions stopped before they began moving in.

Police Chief Joe Mokwa said people were evacuated from a five-block area around the plant. He said there was some concern that unstable chlorine gas could cause a problem.

Authorities say the fire grew for the first hour after it began, sending scraps of cylinders high into the air. The thick smoke, which could be seen for a large area around the fire scene, prompted police to evacuate buildings and businesses for several blocks in the area.

A blaze at an industrial plant sends fireballs shooting into the sky in St. Louis. There were no injuries from Friday's fire, St. Louis Fire Chief Sherman George said. Investigators late Friday still had not determined the cause of the rapid-fire series of spectacular explosions at Praxair Distribution, which processes propane and other gases for industrial use.

The company, city records show, has spent $114,000 on installing fire sprinklers since 1998. Praxair also was issued a building permit for “interior alterations” earlier this year. The firm applied for a business license to operate in St. Louis in 1989, records show, and has 34 employees at that location.

Carolyn Willmore, who lives about five blocks away, was at her home when the explosions began. The blasts were so intense, she said, it caused her windows to bend inward.

“You could see all the windows sucking in,” Willmore said.

Alderman Lewis Reed, whose Sixth Ward includes the plant, was in his office just blocks away when the explosion occurred.

Reed said he could feel the heat all the way from Mississippi Street, about a third of a mile away. Reed said that industrial canisters “literally flew” into the yards of near-by residents.

“Just huge chunks of metal,” Reed said. “Debris just zooming across the sky. I have never, ever seen anything like that in my life.”

The fire began with one explosion followed by a series of loud blasts, Reed said.

Praxair has 27,000 employees and operations in 40 countries, with annual sales of $6.6 billion. It supplies atmospheric, process and specialty gases, high-performance coatings, and related services and technologies.