PORT WENTWORTH, Georgia (CNN) -- The bodies of four workers were discovered Friday in the ruins of a sugar refinery near Savannah, Georgia, that was gutted by a massive explosion and fire Thursday night, and at least four other people are missing, authorities said.
The bodies, which were taken to a medical examiner's office, have not been identified.
"This is still a very fluid situation, there could be more [victims]," said Sgt. Mike Wilson, a spokesman for the Savannah-Chatham Metropolitan Police Department.
Earlier, a reporter asked him about reports that as many as 17 people might be missing.
"I don't want to speculate with a number right now," Wilson said.
Dozens of people were injured, some critically, in the blast.
Firefighters were making a second sweep through the plant in Port Wentworth to look for victims, but it was slow going, said Capt. Matt Stanley of the Savannah Fire Department.
The plant has several hundred thousand square feet, and several floors had collapsed.
The fire was under control, but not out, and there would be hot spots for days, Stanley said.
More than 8 inches of water swamped the lower floors, Wilson said. He told reporters that plumbing pipes burst, and more water poured down when sprinkler systems were activated. The water was being pumped out, Stanley said.
Stanley said it was possible that sugar dust from the refining process had ignited, sparking the blast. Watch Stanley describe the inferno »
"The managers of the refinery believe that it may have been sugar powder -- when that is aerosolized, it can get ionically charged and light off with just a bit of static electricity," Stanley said. "It's very rare, but it can happen." See how sugar dust can turn into a fireball in an instant »
A company executive had no comment on the cause of the blast Friday.
"Our hearts go out to everybody who has been impacted by this," said John C. Sheptor, president and chief executive officer of Imperial Sugar, who was in the refinery at the time of the explosion.
Workers began removing debris Friday morning, Savannah Police Chief Michael Berkow said.
"The structure is very unsafe to enter, and so what we are doing is starting to remove debris very carefully with the assistance of some structural engineers," Berkow said at a news conference attended by other officials. Watch a rescuer describe how he used bolt cutters to prevent a possible second explosion »
He said support centers for families and friends have been set up at the hospitals where the injured were taken, and at the plant site.
The refinery exploded Thursday night, and the blast was so powerful, it shook homes miles across the Savannah River in neighboring South Carolina.
"There was an explosion into the air with debris and a fireball that was probably five or six times as tall as the tallest trees here," said Lt. Alan Baker of the Port Wentworth Police Department. "It's the biggest explosion I've ever seen in my life."
Investigators said they believe the disaster started in a room where workers bag sugar.
Baker and his wife, Joyce, were at nearby City Hall when the blast "shook the ground," he told CNN's "American Morning."
Joyce Baker, who teaches first aid for the Red Cross, said she raced to the scene and pitched in.
"It was like walking into hell," she said.
"We had approximately 13 men who were coming out [of the plant], and they were burned -- third-degree burns on their upper bodies," she said. "And they were trying to sit down, and the only thing that they wanted to know was where their friends were."
Sixty-two people were taken to Savannah-area hospitals, said Buzz Weiss, spokesman for the Georgia Emergency Management Agency. Watch how the effort went from rescue to recovery »
Ambulances and emergency workers from 12 counties had been called in to help, Weiss said.
Doctors were notified about the explosion at 8 p.m. and put together a response team that headed to Savannah Memorial Hospital, said Dr. Fred Mullins, medical director for Joseph M. Still Burn Center in Augusta.
After evaluating the injured, 17 people with burns over more than 30 percent of their bodies were sent to Still Burn Center. The Medical College of Georgia received two patients, Mullins said. Eight patients have burns over 60 percent over their bodies, he added.
Georgia Gov. Sonny Perdue expressed his sympathy in a written statement Friday.
"Mary and I are deeply saddened by yesterday's devastating explosion that has shaken our coastal community," he said. "I want the families of all of those lost, missing or injured to know that they are in our thoughts and prayers."
The U.S. Coast Guard closed the Savannah River around the port, and Coast Guard helicopters searched the water for people who may have been thrown by the blast.
Flames burned overnight and spread from a main building to other parts of the refinery, Stanley said, describing the site as resembling a "small war zone."
He said firefighters were trying to keep the fire from spreading to other parts of the facility where there are flammable materials.
The Savannah Fire Department used a tugboat to pump water onto the blaze from the Savannah River.
The refinery is the major employer in the riverside town just northwest of Savannah.
In October, the U.S. Department of Labor issued new inspection guidelines for workplaces that handle combustible dust particles, including sugar dust.
Plants where a lot of sugar dust is present are classified by the U.S. Occupational Safety and Health Administration as "hazardous locations," the same classification as coal preparation plants and producers of plastics, medicines and fireworks, according to the OSHA Web site. E-mail to a friend