A cargo plane crashed on Sunday at Denali National Park in the U.S. state of Alaska, causing casualties, a park spokesperson said.

It was not immediately known the exact number of fatalities because "the plane pretty much disintegrated," the park's spokesperson Kris Fister was quoted by local media as saying.

The aircraft, which went down near the park's northern border at about 3:15 p.m. local time, is believed to be a twin-engine cargo plane, local KTUU television station reported, quoting National Transportation Safety Board investigator Clint Johnson.

Johnson said investigators will be sent to the scene Monday and military officials said none of their planes were involved.