The two machines — named Dennis and Lea to represent the neighbourhoods of Mount Dennis and Leaside — will dig the underground portion of the line, heading east toward Yonge Street at a rate of approximately 10 to 15 metres a day.
Traffic on Eglinton Avenue near Keele Street was down to one lane in each direction by midday, according to CBC reporter Shannon Martin.
A second pair of tunnel-boring machines, named Don and Humber, will eventually begin digging westward from Leslie Street.
- Metrolinx animation of the Eglinton Crosstown LRT tunnelling
The province has billed the project as its largest public transit construction project in more than half a century, and says the line will help to ease congestion and create thousands of jobs.
"Our government is moving forward with the largest transit investment in a generation to get the region moving," Ontario's transportation minister Glen Murray said in a press release.
"The new Eglinton Crosstown LRT line will get commuters to work, school and play faster than ever before — up to 60 per cent faster than today."
Expected to be in service by 2020, the entire Crosstown LRT line will span 19 kilometres along Eglinton Avenue with a little more than 10 kilometres underground.
The line, which will include up to 25 stations, will link to 54 local bus routes, three TTC interchange subway stations and GO Transit.