The main gas line supplying Morrinsville has been ruptured causing a major gas leak in the Waikato township.

Northern fire shift manager Jaron Phillips said the 100mm pipeline that provided gas to the town had been severed adjacent to Anzac Ave.

The incident, which was unfolding, happened around 12.07 pm.

Fire crews were at the scene and gas contractors were on their way to stem the highly flammable substance, he said.