A river of lava flows down from Mauna Loa, near Hilo, Hawaii.

Watch: Spewing lava and hot ash from world's largest active volcano

The world's largest active volcano burst into life for the first time in 40 years, spewing lava and hot ash.

The world's largest active volcano burst into life for the first time in 40 years, spewing lava and hot ash.

Rivers of molten rock could be seen high up on Mauna Loa in Hawaii, venting clouds of steam and smoke at the summit on Big Island and sparking warnings the situation could change rapidly.

Pressure has been building at Mauna Loa for years, according to the United States Geological Survey, which reported the eruption could be seen from 72 kilometres away.