A bear injured two hikers on a trail at Yellowstone National Park this week, prompting closures of some areas, park officials said Tuesday.

The National Park Service said in a statement that the hikers were injured Monday by “one or more bears” and that the attack was under investigation. More details were not immediately released Tuesday.

The attack happened on Mystic Falls Trail near the ever-popular Old Faithful geyser in Wyoming, the park service said.

In video recorded by Craig Lerman, another hiker, a man can be seen lying on the ground with apparent facial injuries and wearing a blood-soaked shirt. Lerman tells him, “They’re coming,” to which the man replies, “How long?”

Another video shows someone on the ground being helped, and another shows someone being airlifted.

It was the first time a bear has injured someone in Yellowstone National Park this year, the park service said.

The last time someone was injured was in September, the agency said, but it has been over a decade since a bear killed someone in the park.

Lance Crosby, 63, was killed by a grizzly bear in Yellowstone in August 2015.

Some trails and other parts of the park have been closed after Monday's attack, the park service said in a statement.

Seasonal park employee Marie Jaskula, who saw the victims being put onto stretchers, said the attack was sobering.

“It’s very much a reality check,” Jaskula said. “And we have read a quote once, that once you enter the forest, you become a part of the food chain — and it’s very realistic.”