He said contractors had been doing excavation and digging on the footpath when they hit one of the gas mains.
"According to them, the plan they were following showed the gas line going in a straight line, but it does a bit of a dog-leg and unfortunately they've just clipped it."
Mr Cunningham said fire crew isolated and evacuated the area and waited for gas company workers to arrive to shut the gas off and carry out repairs.
He said the gas line contained compressed natural gas, which he said disperses quite quickly.
Mr Cunningham said the main risk was if the gas got trapped in an area, such as a building, an ignition source could spark a blaze.
As a precaution, crew had their hoses laid out on the road ready and the firemen removed their radios and other electrical equipment.
Fire crews starting packing up the cordon about 12.10pm.
Northland Pathology lab manager Will Hermans was one of a handful of people who were standing at the end of the cordon.
He said he smelt gas from their building, which is two doors down from the site where the gas was leaking.
"We checked with the guys [contractors] outside, and made the call to evacuate."
He said about 30 staff from the laboratory had gone to the nearby Whangarei Central Library to have a coffee while they waited for the cordon to be lifted.
Rust Ave Pharmacy owner Helen Guy had also taken her team to the library.
She said a staff member at Northland Pathology had phoned them and told them they should evacuate. She was philosophical about the ordeal, and said accidents happen.
The roadworks are part of the construction for the shared path which will link Rust Ave with Station Rd, Kamo. It will be part of a wider network of cycleways in Whangarei.
Whangarei District Council roading manager Jeff Devine said prior to excavating, contractors Broadspectrum contacted all services including gas and were initially told no gas mains were present.
"Today another team of experienced operators were instructed to prepare foundations for the new street lights and hand dug down 500mm to expose newly installed services and ducts."
He said once all known services were exposed, Broadspectrum proceeded with machine excavation and unfortunately damaged the unknown gas pipe.
"Emergency procedures were followed and a full investigation will now be carried out."