An explosion erupted at a Central Bank of Nigeria office in southern Nigeria Friday afternoon, with reports of several wounded and others feared dead. The building in Calabar, the capital of Cross River state, was under reconstruction at the time of the blast, and several workers suffered severe burns from the flames.

“I could count up to seven people with serious burns,” a source at the nearby University of Calabar Teaching Hospital told local newspaper Premium Times.

Firefighters extinguished the blaze and rescued people trapped inside the building. An official with Nigeria’s Federal Fire Service on scene told local newspaper Vanguard that the source of the explosion was not known.

“I cannot give exact figures of how many people are dead, but many people were burnt beyond recognition while many sustained third-degree burns; rescue operation is going on to ensure everyone is brought out soon,” the official said Friday.

Central Bank of Nigeria spokesman Isaac Okorafor confirmed the explosion with San Francisco-based Nigerian news site THEWILL. Okorafor denied speculation of a bomb attack, saying the blast occurred when a gas cylinder caught fire.

“There is a gas explosion from the construction area of our premises there. There is no fatality yet. A few persons who were injured have been taken to the hospital. The fire service personnel responded promptly and they have been able to put out the fire,” Okorafor said.

A Calabar resident who works less than a half-mile from the bank also said the explosion was not from a bomb blast. He was evacuated shortly after the blast around noon local time and saw emergency teams on site at the nearby central bank office, where wounded workers were rushed to the hospital for treatment. He returned to work once security officials gave the all-clear of his office building.

"The effect was felt around my office, as we were juggled up by the vibration of our building," said the resident, who spoke to International Business Times on condition of anonymity because he did not have permission from his job to speak to the media. "People with various degrees of injuries were brought out [of the central bank office] and rushed to the teaching hospital. Two people were brought out in what looked like a lifeless body."

The explosion comes one day after the Central Bank of Nigeria announced it had suspended key members of its staff involved in a fraudulent transaction uncovered by management. The incident was reported to the authorities, the central bank said in a press release Thursday obtained by Nigerian newspaper PUNCH.

“A highly sophisticated plot to defraud the CBN by some criminally minded elements has been uncovered and aborted by the bank,” the statement said. “Although preliminary investigations so far have not revealed any accomplices within the CBN, the management has decided to place all key personnel involved in the transaction on suspension.”