Scientists have reached Antarctica's largest icebound freshwater lake hidden for millions of years under miles of ice.

A team from Russia's Arctic and Antarctic Research Institute reached Lake Vostok on Sunday after more than two decades of drilling.

The discovery has been avidly anticipated by scientists around the world, who hope that the lake, comparable in area to Lake Ontario, may contain microbial life and provide a clue in the search for life on other planets in similar conditions.

The project has drawn fears that lubricants and antifreeze used in the drilling may contaminate the pristine lake.

Russian researchers have argued that the water from the lake would rush up the borehole driven by a jump in pressure, safely sealing pollutants.

The breakthrough may also provide precious material that would help look for life on ice-crust moons of Jupiter and Saturn or under Mars' polar ice caps where conditions could be similar.

"There is no other place on Earth that has been in isolation for more than 20 million years," said researcher .

"It's a meeting with the unknown."

He said that scientists hope to find primeval bacteria that could expand the human knowledge of the origins of life. "We need to see what we have here before we send missions to ice-crust moons, like Jupiter's moon Europa," he said.

Lake Vostok, about 2.4 miles beneath the surface, is the largest in a web of nearly 400 known subglacial lakes in Antarctica, and scientists in other nations hope to follow up with similar projects.