At least seven people were injured, four of them suffering serious burns, in a gas explosion Wednesday at a supermarket in Rio de Janeiro, firefighters said.

The blast, which occurred about 7:30 a.m. (9:30 GMT), apparently was caused by a gas leak at a grocery store in the northern Rio neighborhood of Iraja, the Fire Department said.

The victims were in the store's bakery at the time of the explosion.

Four of the victims suffered third-degree burns and were taken to two nearby hospitals.

"For now, we know that apparently there was a gas leak, but only the investigation will determine the causes of the explosion. The gas cylinders were not affected and are in the correct position," said firefighters Lt. Col. Marcelo Leite, who is in charge of the operation.

He added that the material damage was minor and first assessments were that the building was experiencing no structural problems.

Supermarket employees told reporters that they had been smelling a strong odor of gas at the store for at least the past two weeks. EFE