READ THE LATEST IN THIS STORY: Bear won't be put down in Alberta grizzly attack

A grizzly bear attacked a young woman northwest of Calgary Tuesday morning, according to paramedics and witnesses.

"We were bringing some hay up and we looked into the valley and we saw someone jump in the river and a bear chewing on someone else," said Coleman Blair, a ranch hand at the Lazy H Trail Company and Trapper's Hill Campground, where police and paramedics responded to the injured woman.

Blair ran down a large embankment towards the scene. The bear had moved away to the other side of the river by the time he reached James Hayworth and his wife, Laura.

"When I got there, she was chewed up pretty bad, and he was, I think, shook up as well," said Blair.

The man who helped rescue a woman and her boyfriend from a mother grizzly today said the couple probably just surprised her. 0:35

STARS Air Ambulance said a 25-year-old female patient was transported from the MD of Bighorn to Foothills Hospital in Calgary in stable condition.

James Hayworth later told CBC News that Laura has a broken arm and multiple puncture wounds, while he has scrapes, cuts and bruises, including a paw print on the back of his hamstring from where the bear stood on top of him.

"About 99 per cent of the time I have a rifle on me, today for some reason I didn't bring it with me," said Blair.

"You know, you see people getting chewed on, you can't really stand around."

The bear was a female grizzly with two cubs, but the cause of the attack is not known at this time.

Ron Wiebe, an inspector with the Fish and Wildlife Enforcement branch, said from what he understands, the victim and a man were having a picnic by the river when the incident occurred.

He said bear attacks "aren't that rare" in the area.

"We've had, in the last number of years in this area, we've probably had close to half a dozen in this immediate area, we've had people bitten and people bluff charged and some people chewed on a little more serious than others," said Wiebe.

The approximate site of Trapper's Hill Lodges, where police and paramedics responded to the woman who was injured in an apparent grizzly bear attack. (CBC)

He said his officers have taken some clothing to obtain DNA samples in case they need to determine the specific bear involved in the attack and what to do with it.

"In the case of a female and cubs we're always a little cautious," he said. "We don't want to be running in and taking a bear out of this ecosystem if it's essential here."

Wiebe said the area will be closed for a "significant amount of time."

Waiparous Village is about 70 kilometres northwest of Calgary.