Four tunnel boring machines have begun their work on the TTC's Spadina subway extension, which will allow riders in Vaughan to access Toronto transit.

TTC Chair Karen Stintz was among the politicians representing various levels of government at Downsview Park Friday morning to officially kick off the tunnelling process.

"We are about to begin one of the biggest digs ever to extend the Spadina subway into new places right into the 905 region of York. If we build it, they will come," she said.

"It is a great and historic day for commuters who rely on public transit to get to work and to get home again - or to get to school and get home again,"

The tunnel boring machines — officially named Holey, Moley, Yorkie and Torkie — will move at a pace of about 15 metres a day, although that is dependent on soil conditions. The $2.6-billion extension is expected to be completed by late 2015.

The 8.6-kilometre extension of the Yonge-University-Spadina line moves it northward from its current endpoint at Downsview station past Toronto's city limits into the Vaughan Metropolitan Centre at Highway 7.

Among the six new stations that will be built is one at the Keele campus at York University, which is attended by just under 50,000 full- and part-time students.

The funding for the project comes from governments at all levels, including: