TAVARES, Fla. -

Eight people were injured -- four critically -- late Monday night in a series of massive explosions at a Blue Rhino propane facility in Tavares.

PHOTOS:  Explosions rock propane plant in Central Florida

The blasts, which continued for about four hours, began around 11 p.m. at the gas plant, which is located on County Road 448, prompting evacuations of homes and businesses within a mile of the facility.  The evacuation order was later lifted.

About two dozen workers were at the plant when the explosions occurred and all were accounted for after it was initially believed that 15 employees were missing or trapped.

Lake County Sheriff Gary Borders said the blasts occurred inside the plant and blew the roof off the building.  The explosions were so big that they showed up on radar, with a green swath showing the change in temperatures.

Aerial footage of the scene early Tuesday morning showed fires burning over a large area, with flames and plumes of smoke shooting into the night sky.

More than 50,000 propane cylinders -- similar to ones used for back yard grills -- were scattered throughout the plant and caught fire, each exploding into the air.  Witnesses said the 20-pound tanks shot up to 300 feet in the air.

"At one point in time it was really big.  Then it dies down and then about 5 minutes ago, it blew up.  It blew up again even worse, so hopefully it'll keep dying down," said witness Cody Rhoades.  "You can see the flames and all of a sudden (there was) a loud boom -- propane tanks blowing up.  You just see it going and flames at one point, just a minute ago, you could feel the heat going off the fire.  It was way hot."

Bobby Hutsenpiller, who was on the job for the first time, was less than 100 yards from the first explosion inside the facility.

"I was so scared.  I didn't want to look back," said Hutsenpiller, who added that he ran for his life.

The cause of the blasts is under investigation, but Tavares Fire Chief Richard Keith said Tuesday morning that it's not believed to be an act of sabotage.

"We think it's equipment failure with a combination of possible human error," said Keith, adding that the state fire marshal will likely conduct an investigation.

"It's a scary situation when you fear something like that and then it actually happens," John Bogdan said.  "I didn't know what it was at first.  I thought maybe the lumber place (a nearby business) got on fire, then we started seeing those grill tanks, gas tanks, flying up in the air, and it literally had to be at least 200 to 300 feet in the air.  The first explosions really rocked the house."

The injured workers were taken to several area hospitals.  No first responders were injured in the incident.

The Blue Rhino plant in Tavares was established in 1994 and refills and distributes 20-gallon tanks of propane.  The facility cleans used tanks, refinishes them and refills them before sending them back to stores.

Tavares is about 40 miles northwest of Orlando.