There is no subway service running between Islington and Ossington stations on the west end of Line 2 early Tuesday, the TTC says.
A spokesperson for the transit agency said work being done to install a new piece of rail in the area of High Park Station overnight was delayed, forcing a shutdown on a long stretch of track.
Shuttle buses are running from Kipling to Ossington, according to the TTC.
The spokesperson could not say when regular subway service may resume.