The offspring of Indonesia's infamous Krakatoa volcano erupted on Sunday, spewing a towering volcanic ash cloud some 3,000 metres (9,800 feet) into the sky.

Mount Anak Krakatoa, which means Child of Krakatoa, belched thick ash over the strait that separates the islands of Java and Sumatra forcing authorities to warn nearby residents to wear masks outside.

"We are still recording continuous eruptions with thick clouds towering at between 500 to 3,000 metres from the peak," Deny Mardiono of Indonesia's Geological Agency told AFP.

Anak Krakatoa has erupted at least 21 times in recent weeks but Sunday's eruption was the largest yet, Mardiono said.

Authorities ordered people to stay out of a two-kilometre exclusion zone around the volcano, which is currently graded at level two of Indonesia's four-tiered volcanic alert system.

Anak Krakatoa, which means Child of Krakatoa, is currently on level two of the country's four-tiered alert system
Anak Krakatoa, which means Child of Krakatoa, is currently on level two of the country's four-tiered alert system AFP / DZIKI OKTOMAULIYADI

"People, including tourists, should adhere to the recommendation from the Geological Agency, which prohibits anyone to be within a two-kilometre radius from the crater," he added.

The volcano has been sporadically active since it emerged from the sea at the beginning of last century in the caldera formed after the 1883 eruption of Mount Krakatoa.

That disaster was one of the deadliest and most destructive in history with an estimated 35,000 people killed.

Anak Krakatoa last erupted in 2018, generating a tsunami that killed 429 people and left thousands homeless.

Indonesia, a Southeast Asian archipelago nation, sits on the Pacific Ring of Fire where the meeting of continental plates causes high volcanic and seismic activity.

The country has nearly 130 active volcanoes.