An intense fire at a Venezuelan refinery spread to a third fuel tank on Monday nearly three days after an explosion killed at least 41 people and injured more than 150.

Oil Minister Rafael Ramirez said the third tank ignited at the Amuay refinery, which has been in flames since Saturday's blast.

Government officials had previously said they had the blaze contained, and the spread to another tank was an apparent setback to their plans to quickly restart the refinery. While a thick column of smoke blew in the wind, Ramirez told reporters the fire was still contained.

"There is no risk of a bigger event," Ramirez said, without specifying how much longer it might burn.

Officials have said a gas leak led to the blast, but investigators have yet to determine the precise causes. Prosecutor General Luisa Ortega said at a news conference that 151 people were injured, 33 of whom remain in hospitals.

A 9-year-old girl was missing in the area, Health Minister Eugenia Sader said on television.

Criticisms of the government's response to the gas leak emerged from local residents as well as oil experts. People in neighborhoods next to the refinery said they had no official warning before the explosion hit at about 1 a.m. on Saturday.

"What bothers us is that there was no sign of an alarm. I would have liked for an alarm to have gone off or something," said Luis Suarez, a bank employee in the neighborhood. "Many of us woke up thinking it was an earthquake."

The blast knocked down walls, shattered windows and left streets littered with rubble.

People who live next to the refinery said they smelled strong fumes coming from the refinery starting between 7 p.m. and 8 p.m. Friday, hours before the blast, but many said they weren't worried because they had smelled such odors before.

Then, a cloud of gas ignited in an area with fuel storage tanks and exploded.

President Hugo Chavez visited the refinery on Sunday. In a televised conversation with the president, one state oil company official said workers had made their rounds after 9 p.m. and hadn't noticed anything unusual. The official said that at about midnight officials detected the gas leak and "went out to the street to block traffic."

"And later something happened that set (it) off," Chavez said. "A spark somewhere."

Chavez visited some of the wounded in a hospital on Monday and said that more than 500 homes were damaged.

The disaster occurred little more than a month before Venezuela's upcoming Oct. 7 presidential election. Opposition candidate Henrique Capriles said the tragedy shouldn't be politicized, but he also strongly criticized a remark by Chavez, who had said "the show should continue, with our pain, with our sorrow, with our victims."

"It seems irresponsible, insensitive... to say 'the show should continue,'" Capriles told reporters in Caracas. He repeated past criticisms about the number of accidents at the state-owned oil company, and called for "a serious, responsible and transparent investigation."

"The state has to give answers. Venezuelans have a right to know what happened in Amuay," Capriles said.

Energy analyst Jorge Pinon said the accounts of the hours leading up the explosion raise concerns.

"The fact that the gas leak went undetected for a number of hours and that there was no evacuation alarm (or) order indicates to me that there is a lack of safety related planning and behaviors throughout the complex, and most important in nearby communities," Pinon said.

"The key to refinery safety is not only equipment and maintenance but processes and behaviors," Pinon added, "not only within company employees but also contractors and surrounding communities."

U.S. refineries have also had their share of serious accidents, most recently the destructive blaze at Chevron's refinery in Richmond, California.

Some experts say that U.S. refineries have increasingly used more sensing systems to alert workers to gas leaks, and also have established safety protocols.

In the Houston area, for instance, "there are 10 or 11 different community groups that the various industries meet with frequently. They stay pretty well connected, with a set agenda," said Alex Cuclis, a research scientist at the Houston Advanced Research Center who used to be a refinery engineer.

"They have a phone number to call. And the industry can and occasionally does set off alarms to 'shelter in place,' and most who live in the communities know that means shut off air conditioners so that they aren't bringing in outside air," Cuclis said.

Amuay is among the world's largest refineries and is part of the Paraguana Refining Center, which also includes the adjacent Cardon refinery. Together, the refineries process about 900,000 barrels of crude per day and 200,000 barrels of gasoline.

Esteban Mosquera, who lives near the complex, said there have been many other incidents at the refineries, including smaller fires and power outages.

"We know the risks of living beside a refinery, but here the accidents in recent years have been very frequent," Mosquera said.

At least two dozen incidents have been reported at the refinery complex since 2003, including power outages, fires and explosions. In January 2009, a fire at the Cardon refinery injured at least seven firefighters and refinery workers.

Thomas O'Donnell, an international energy researcher at The New School in New York, said it's not possible to say whether the explosion was linked to poor maintenance.

"However, one can say that this is one in a series of all-too frequent accidents at this and other Venezuelan refineries over the past approximately five years," O'Donnell said.

Ivan Freites, a labor leader and employee who works at the refinery, said he and other workers had warned earlier this year that safety situation was precarious after a series of incidents including leaking pipes, fires and shutdowns of equipment. "The tragedy could have been avoided," he said.

Chavez and other government officials deny that, saying billions of dollars have been spent in recent years to keep the country's refineries properly maintained.


Associated Press writers Ian James and Fabiola Sanchez in Caracas contributed to this report.