Hydro One is launching a 150-thousand-pound tunnel boring machine today to build a new tunnel under Toronto's downtown core.

The provincial utility says it's launching the Celtic Tiger Tunnel Boring Machine this afternoon at its Esplanade Transmission Station.

The Celtic Tiger will spend a year boring a 2.5 kilometre tunnel underneath the city core, excavating dirt, soil, concrete and other material.

The new tunnel will run approximately 26 metres underground and will house new transmission cables for the city's --quote-- "most critical institutions, including Hospital Row, City Hall and the Financial District."