Watch: Tourists too close for mum to bear

The mamma bear appears to charge several people, unleashing a frightening burst of speed. Photo / AP

A mother bear and her cubs gave tourists in America's Yellowstone National Park a sharp refresher in the rules on how to appreciate the wildlife - stay a safe distance and never take them for granted.

The photo-snapping tourists found themselves running for safety after they got too close to the family of black bears, upsetting the animals, according to the Montana Fish, Wildlife and Parks service.

The incident, which was captured by a videographer who works for the service, shows some tourists running for their vehicles while others try to stay out of the way. At one point, the zigzagging mamma bear appears to charge several people, unleashing a frightening burst of speed.

"Keep moving!" a man can be heard yelling. "Go! Go!"

Bob Gibson, communications and education programme manager with the Montana service, told the USA Today newspaper the tourists were "very much in danger".

"The most dangerous place is between a [mother] and her cubs," he said.

Coming into close proximity with a bear will point up very quickly how limited your options are. You can't outclimb or outrun a bear, even if you're travelling downhill, experts say.

Gibson told the newspaper the cubs were about 13 months old and he noted the mother was not as aggressive as she could have been if they were newborns.

"If they had been born in the last few days, it could have been much worse," he said, adding that people should stay at least 100m away from bears.

- additional reporting Bloomberg