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Over 45,000 people have applied to cull bison in the Grand Canyon after the US National Park Service (NPS) requested volunteers to help with overpopulation.

The famed national park in Arizona is seeking 12 "skilled volunteers" to reduce the herd, which has grown large enough to cause environmental damage.

The event is not being classified as a "hunt", as hunting is forbidden in US national parks.

Some environmentalists have warned the move could set a dangerous precedent.

The lottery opened on Monday and closed after 48 hours with 45,040 applicants.

An initial 25 names will be selected. After being vetted by park officials for skills including marksmanship, 12 people will be given the opportunity to kill a bison in the park's North Rim area.

Volunteers are permitted to bring a support crew along, . Bison can weigh over 2,000lbs (900kg), but the sharp-shooters must carry out any meat on foot without the help of motorised transport or pack animals.

The event will take place in rugged, rocky and sometimes snowy terrain, with elevations exceeding 8,000ft (2,440m).

Officials say the pilot programme is required after the herd rapidly grew to 600 bison in recent years. The NPS hopes to bring the herd residing on the North Rim down to about 200 in order to reduce trampling of Native American archaeological sites, soil erosion and water contamination.

Before being hunted to near-extinction in the 19th Century, bison (which are also known in the US as buffalo) roamed across much of the continent. An estimated 30 to 60 million bison were reduced to only about 400 by the late 1800s.

But environmentalists say there is little evidence that the Grand Canyon was ever part of their historic range.

According to historians, the North Rim herd was introduced to the area after to interbreed bison with cattle in the early 1900s.