A family got a little closer to nature than they bargained for when a bear opened their car door at Yellowstone National Park.

Footage posted on YouTube this weekend shows the family's encounter with a bear wandering near the side of the road.

As they photograph the animal, it becomes clear that they've forgotten one important thing - to lock their doors.

"Dad, the bear's right next to us," a young boy can be heard saying nervously.

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Somehow, the bear manages to open a door, while children scream loudly in the back seat.

The man driving the car manages to pull the door closed, but it is clear that it took a lot of effort to do.

The bear break-in is just the latest in a series of strange and foolish incidents at Yellowstone this year.

Last month, a baby bison had to be euthanised after well-meaning tourists became concerned for its safety and transported it to a ranger station in the back of their SUV.

Only days later, a group of Canadian YouTubers - including one New Zealander - were hit with criminal charges for walking on an off-limits geyser in the park.

Earlier this month, video footage showed a tourist being charged at by an elk in Yellowstone, after getting too close for a photograph.

The park recommends visitors stay at least 90 metres away from bears and wolves and at least 22 metres away from all other large animals, including bison, elk, bighorn sheep, deer, moose, and coyotes.