An explosion caused by a gas leak rocked the French city of Lyon on Thursday, killing a firefighter and injuring 35 people, two of them seriously, police said.

A large number of firefighters were dispatched to the scene on the Cours Lafayette shopping street in the heart of Lyon where the blast occurred around midday during maintenance work on an underground gas pipe.

Fire engulfed several buildings in the centre of France's third biggest city and police evacuated close to 1,000 people from the area.

A 35-year-old firefighter, father of two children, who was investigating a leak of gas into the basement of a building, was killed in the blast, said Lyon Mayor Gerard Colomb.

Interior Minister Michele Alliot-Marie, who travelled immediately to the scene, told reporters that lax security was partly to blame.

She said she was sorry that "all the security procedures were not sufficiently taken into account" and pledged to find ways to boost safeguards for gas maintenance work.

Two people were seriously injured in the blast, including an employee of gas utility GDF, who suffered lung damage, medical officials told AFP.

The other injured, most of whom suffered minor scrapes, were evacuated to nearby hospitals, according to the local prefecture.

The explosion occurred less than an hour after the gas leak was reported to firefighters, officials said.