A fire broke out at a petrochemical plant in southern France after two explosions in the early hours of Tuesday morning, officials said.

"It broke out on Tuesday morning at the LyonDellBasell oil refinery in the town of Berre l'Etang after two tanks, 500 meters apart from each other and filled with chemicals are exploded," an official source said, according to Xinhua news agency.

The two explosions were heard at the plant at 3 a.m. local time (0100 GMT) on Tuesday morning as the country began celebrations of its national Bastille Day. However, no injuries were reported

An investigation launched into the incident, which occurred close to Marseille Provence Airport in southern France. Investigators believed the explosions were the result of "a malicious act," a source close to the investigation told Agence France Presse. "The probability that these two fires in tanks 500 metres (1,640 feet) apart could be accidental is very low. Investigators are leaning towards the theory of a voluntary act," an informed source said.

"The simultaneous explosion of the tanks, which are spaced about 500 metres (yards) from each other, is not the result of a technical accident. The thesis of criminal intent is clearly being considered," a source close to french authorities told Reuters.

The French government ruled out any possibility of health risk from toxic smoke. "The type of combustion of the smoke does not represent a risk of toxicity, only in cases of long-term exposure which is not the case in today's blasts," French energy ministry said, according to Anadolu Agency.