A fracture to a mains pipe in Glensburgh Road, Grangemouth, led to a release of gas, and a 100-metre cordon has been erected while emergency repairs are carried out.
Premises near the site of the leak have been evacuated as a precaution and the off-ramp at junction six of the M9 motorway has been closed along with the A905 road, police said.
A spokeswoman for the fire service said: "The incident commander immediately requested a 100-metre exclusion zone to ensure the safety of the public with the assistance of Police Scotland colleagues.
"Evacuation of surrounding premises has also been undertaken as a precautionary measure.
"At the same time one large water curtain spray and one large firefighting jet were set up to assist in the dispersal of the escaping gas."