Police and fire crews are now at the scene at the Maryville Interchange, just off Junction 1 of the M73 at Uddingston.
A spokeswoman for Scottish Gas Networks confirmed workers are investigating but had no further details.
She said: "Teams are on site assessing the situation and we will issue an update when we have more information."
A spokeswoman for Police Scotland confirmed officers are at the scene.
The Scottish Fire and Rescue Service said three appliances and the Environmental Protection Team from Hamilton are also at site.
The motorway is believed to be down to one lane while staff carry out an inspection of the area.
Drivers are warned to expect delays.
One motorist said a strong smell of gas was in the air as far away as Blantyre.
Police were slowing traffic at the scene, behind the Bargeddie Industrial Estate, and only allowing lines of around 20 cars to pass at any one time.
The driver said: "We were heading out from Glasgow and you could smell the gas all the way from Blantyre.
"The roar of the gas is really loud as well - I haven't heard anything like that before.
"Traffic is not as bad as I would expect but it is moving very slowly and holding people up."