NEW NASA photo reveals the lava lake on Australia's only active volcano has overflowed the crater, showing possible signs of eruption.

NASA's EO-1 satellite snapped the shot of Big Ben, which is located on the remote Heard Island, about 4,100km southwest of Perth, in the sub-Antarctic, on April 20.

When compared to another image taken on April 7, it appears the lava flow is widening at the top, NASA said.

The volcano's caldera appears to have filled with so much lava that some has since cascaded down Mawson Peak.

Heard Island's remoteness and Mawson Peak's altitude of 2745 metres mean there's nothing to fear from the eruption, The Register reports.

No permanent human presence exists on the island, beyond an automated weather station.