Police are looking for two suspects, named as Damien Sanderson and Myles Sanderson, who are on the run and considered armed and dangerous.
The stabbings took place in several locations on the James Smith Cree Nation and in the village of Weldon, north-east of Saskatoon, police said.
Rhonda Blackmore, assistant commissioner of the RCMP Saskatchewan, said some of the victims appear to have been targeted by the suspects, but others appear to have been attacked at random.
She could not provide a motive.
“It is horrific what has occurred in our province today,” Ms Blackmore said.
She said there are 13 crime scenes where either dead or injured people were found.
The search for suspects was carried out as fans descended on nearby Regina for a sold-out game between the Canadian Football League’s Saskatchewan Roughriders and Winnipeg Blue Bombers.
The Regina Police Service that with the help of the Mounties, they were working on several fronts to locate and arrest the suspects and had “deployed additional resources for public safety throughout the city, including the football game at Mosaic Stadium”.
Checkpoints have been set up across the central Saskatchewan province, with residents urged to shelter indoors.
The Saskatchewan Health Authority said patients were being treated at several sites.
“A call for additional staff was issued to respond to the influx of casualties,” authority spokeswoman Anne Linemann said.
Mark Oddan, ambulance service spokesman, said two helicopters were dispatched from Saskatoon, Saskatchewan and another from Regina.
Prime Minister Justin Trudeau described the attacks as "horrific and heartbreaking".
"I am shocked and devastated by the horrific attacks today," he said in a statement. "Those responsible for today's abhorrent attacks must be fully brought to justice."
A state of emergency was declared in the James Smith Cree Nation - an community of about 2,000 residents north-east of the village of Weldon, which is home to just 200 people.
"Do not leave a secure location. Use caution allowing others into your residence," Saskatchewan Royal Canadian Mounted Police (RCMP) warned people across the vast search area.