REGINA -- A northern Saskatchewan First Nation has been locked down and its schools closed over concerns of COVID-19 transmission following a series of religious services where participants were unmasked.

Those gatherings resulted in six COVID-19 cases and at least another five linked to that investigation, said the province's chief medical officer of health Dr. Saqid Shahab.

"We expect those case numbers to go up," he said.

The Saskatchewan Health Authority said Wednesday it was investigating a community transmitted COVID-19 outbreak linked to a series of Full Gospel Outreach events in Prince Albert from Sept. 14 to last Sunday.

The investigation involves contact tracing more than 100 people, including a small number from Alberta and Manitoba, Shahab said.

"I did alert my counterparts last night," Shahab said.

On Thursday, the Peter Ballantyne Cree Nation shuttered its three communities of Southend, Sturgeon Landing and an urban reserve in the city of Prince Albert.

"All vehicles entering the communities will be searched," said a notice from Chief Peter Beatty. "Absolutely no parties will be allowed."

Roadblocks have been erected and non-members and visitors are not allowed into the communities, which are home to about 2,400 people. Only essential services staff may enter.

Residents may leave and return for grocery shopping and medical appointments.

The band has also closed its two schools until at least Oct. 19 because of possible staff exposure to the virus "that may have occurred at a recent funeral and church service," said a Facebook posting from band education co-ordinator Greg Seib.

"This school closure will provide time to thoroughly clean and sanitize the schools and the school buses," Seib's posting said.

Currently in the middle of an election campaign, Saskatchewan Premier Scott Moe said people need to stay virus-vigilant.

"Let's not let our guard down in adhering to the public health recommendations, including wearing a mask if you should be singing in your place of worship," he said Thursday.

Pictures on social media of the worship gathering showed a crowded room with few wearing masks.

Shahab urged people to return to the urgency of the early days of the pandemic and resume following health guidelines.

"We have noticed that in workplaces and other settings, best practices for mask use are not being observed," he said. "We must now return to the behaviours we demonstrated so diligently in March and April."

Shahab said Thanksgiving should be celebrated only among immediate family members.

Generally, worship services have not been a problem, Shahab said.

"Places of worship have been open since March. We have not seen problems."

The province reported 18 new cases of COVID-19 Thursday, bringing the total to 2,012 reported cases.

Public health orders in the province state that indoor and outdoor gatherings may have up to 30 people, as long as there is enough space to maintain social distance between those who aren't in the same household.

This report by The Canadian Press was first published Oct. 8, 2020