One of the youngest and biggest impact craters ever found has been discovered under about a kilometre of ice in Greenland.

Key points: Asteroid believed to have been more than a kilometre wide

Asteroid believed to have been more than a kilometre wide Hiawatha glacier came to researchers' attention in mid-2015

Hiawatha glacier came to researchers' attention in mid-2015 In 2016, a German research plane mapped the depth and topography of the crater

The Hiawatha crater is 31 kilometres in diameter, bigger than Paris, and unlike the sites of some other impacts of this kind, still has a classic crater bowl shape.

It is in the top 25 largest craters discovered on earth and one of the youngest, with researchers saying it was created within the past 3 million years.

Modelling suggested the asteroid was more than a kilometre wide.

Researchers first got a sense of the crater's location in mid-2015 thanks in part to NASA's Operation Ice Bridge, which flew over areas like the Hiawatha Glacier to track changes in polar ice.

A large hunk of an iron meteorite that was found near Hiawatha years ago currently sits in the courtyard of the Natural History Museum in Copenhagen and it was researchers there who drew the connection.

After receiving a new map of bedrock topography under the ice, thanks to two decades' worth of NASA's expeditions in the area, scientists began to look closer at a "conspicuously semi-circular" section of the ice sheet's edge.

A semi-circle on the edge of the ice sheet was a dead giveaway that something was lurking underneath. ( Supplied: NASA )

In May, 2016, a German research plane mapped a depression about 300 metres in depth under that semi-circle.

"The crater is exceptionally well-preserved and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact," lead author of the study Kurt Kjaer said.

They also found the oldest ice in the glacier had experienced a great disturbance towards the end of the last ice age and quartz in the surrounding area displayed evidence of a substantial violent impact thousands of years ago.