Two hikers have been injured in a bear attack on a popular hiking trail near Yellowstone National Park's Old Faithful geyser, park officials say.

The attack was described by officials as a single event on Monday afternoon along the Mystic Falls Trail.

A large area of the park near the Midway Geyser Basin was temporarily closed pending an investigation.

The area includes at least five trails and several back-country campsites.

Park officials said one or more bears were involved but did not specify which species.

The park has populations of both grizzly bears and black bears, which can be difficult to tell apart at times.

Grizzlies can be more aggressive and they grow much larger - as much as twice as big as black bears.

Black bears usually have darker colouring.

Further information - including whether the victims were hiking together and whether they were hospitalised for their injuries - was not being immediately released, Yellowstone spokeswoman Ashton Hooker said.

Yellowstone gets more than four million visits by tourists annually and attacks by grizzlies or black bears are rare.

In September, a hiker suffered injuries to his chest and arm in an attack on the Turbid Lake Trail northeast of Yellowstone Lake, and a grizzly killed a woman just west of Yellowstone in 2023.

The last fatal bear mauling in the park was in 2015 when a 63-year-old Billings, Montana man was killed while hiking alone in the park's Lake Village area.

The fate of bears that attack humans is typically dictated by the circumstances of the encounter.

Following the 2015 fatal attack, officials captured and killed an adult female grizzly because it had eaten part of the victim's body and hid the rest, which is not normal behaviour for a bear defending its young.

By comparison, last year's attack on the Turbid Lake Trail happened during a surprise encounter between the victim and the bear.

The animal's reaction was considered natural, so it was not relocated or killed.

The heavily travelled Mystic Falls trail where Monday's attack occurred includes a loop that leads to a 21-metre-tall waterfall.

The trailhead is about 3km northwest of Old Faithful.