Around 3,500 homes have lost their gas supply after damage to a pipe caused a major leak.
Properties in Fishcross, Dollar and Tillicoultry in Clackmannanshire have been cut off and Fishcross and Clackmannan primary schools were closed as a precaution.
The leak started at about midday when a farmer in Fishcross ruptured a large pipe while doing drainage work in a field, Scotia Gas Networks (SGN) said.
Roads in the area have been closed but police said homes have not been evacuated and the gas level in the air is being monitored.
SGN is working with Central Scotland Police and Fire & Rescue to repair the damage. An SGN spokeswoman said at around 6.15pm: "The situation is changing rapidly but at the moment we have 3,500 homes in the area without gas supplies. We have hundreds of engineers on site and portable appliances are available for cooking and heating."
The spokeswoman said everything was being done to restore supplies and thanked customers for their patience. "It is difficult to be exact as to when the pipe will be repaired but it could take several days," she said.
Clackmannanshire Council said all 69 pupils at Fishcross primary school were collected by their parents or carers following their evacuation.
A smell of gas was also detected at Clackmannan primary school and pupils were evacuated to Clackmannan town hall.
The B9140 road was shut from Collylands to Fishcross and the A908 from Hallpark, Sauchie, was also closed.
Council chief executive Elaine McPherson said: "We are working closely with all our partners to ensure people's safety and that the incident is managed efficiency."