Toronto subway
Commuters have voiced their anger at the quality of Toronto's subway line(REUTERS/J.P. Moczulski

Subway service has resumed in Canada's financial capital, Toronto, after "major communication issues" shut down the city's entire system during rush hour on Monday.

At 6.41am EST on 8 June, radio issues along the city's three subway lines forced trains to a halt.

Stations were evacuated as early as 7am, forcing many of the 900,000 passengers who ride the rails every day to find alternate ways to commute.

Some 158 buses and streetcars make 245 connections with Toronto's Subway and Scarborough rail system during the morning rush each day.

Toronto Transit Commission chief executive Andy Byford told Toronto's mayor John Tory he has "a thorough investigation underway".

Byford took to a Toronto radio station to say that the transit company will issue an explanation for the shutdown later in the day.

Last weekend, service was shut down on the city's main Line 1 as crews worked to upgrade the 60-year-old signal system. The TTC's website said the "necessary signal work will result in a more reliable service".

Many commuters voiced their ongoing frustration with the quality of the city's subway line during the shutdown.

In the past the city has turned to the UK for advice on how to improve its subway infrastructure.

In a scoping report by UK Trade and Investment released in late 2013, the UK government targeted Canadian rail as a market potentially worth billions of pounds to the industry under the new EU-Canada Comprehensive Economic and Trade Agreement.