CALGARY, Alberta - Restrictions imposed by British Columbia to fight the spread of Covid-19 infections after the holiday break have disrupted work at construction sites of a Rio Tinto hydropower project and BC Hydro's Site C dam.

A total of five major industrial projects in remote northwestern Canada have been affected as the provincial government last week ordered them to stagger the return of their workers after the Christmas holiday break.

BC Hydro's Site C dam, Rio Tinto's Kemano T2 hydropower project, the Trans Mountain pipeline expansion, TC Energy's Coastal GasLink pipeline and the Royal Dutch Shell-led LNG Canada project are named in the order.

The companies did not say how the slow return of workers would impact ultimate completion dates for their projects.

Across the five projects the number of workers will ramp up from a baseline of 1,460 to 4,080 by mid-February.

Provincial health officer Dr Bonnie Henry said a rapid return to full operating capacity after Christmas would likely "fuel and accelerate" the spread of COVID-19 among workers and surrounding communities.

"While these changes will have a further impact on our overall project schedule and cost, we understand the rationale for the order," said David Conway, spokesman for the C$10.7-billion ($8.4-billion) Site C project on the Peace river, which is already over budget.

Rio Tinto's Kemano T2 project, in which a second tunnel is being built to provide hydropower to the BC Works aluminium smelter in Kitimat, would normally have 330 workers on site but will be limited to 280 until further notice.

Rio Tinto expects the project to resume operations when it is authorized "to increase the number of workers onsite to safely operate the tunnel boring machine," a company spokesman said.

The Canadian government-owned Trans Mountain project halted work on the pipeline expansion in December after multiple safety issues.

Construction was meant to restart on Monday but is still paused, although Trans Mountain did not say whether the new COVID-19 rules had caused the delay. The 1,150-kilometer pipeline carries crude from Alberta across British Columbia to the coast and the order only affects one work camp in Valemount.

"We are in the final stages of our restart planning and anticipate that we will be providing further details on restart dates in the coming days," a Trans Mountain spokeswoman said on Tuesday.

An LNG Canada spokesman said the slower return to work schedule would enable the project to keep going with "seasonally critical" work. Coastal GasLink did not immediately respond to a request for comment.