Montreal's underground metro system came to a grinding halt Saturday morning because of computer problems.

The breakdown was initially reported just after 10 a.m.

All lines – green, orange, blue and yellow – were disrupted for nearly an hour.

Service was gradually restored to the green, orange and blue lines at 11 a.m.

Montreal's transit authority – STM – dispatched shuttle buses to certain stations.

A similar outage happened June 20 during rush hour, because of computer problems.