Roman, a resident of the area who operates tours to Anak Krakatau, said by text message the weather had been fine when the waves struck, although residents had become wary of the rumbling volcano.

He said many others had taken refuge in his elevated village of Tahura Carita, which is about 100 metres from the sea. Evacuees were relying on instant noodles, he said.

Heavy equipment was being moved in to help with rescue efforts, as well as water and sanitation equipment. The military said it was deploying troops to distribute aid and blankets, as well as sending in medics.

The western coast of Banten province in Java, Indonesia's most populated island, was also badly hit, said Sutopo Purwo Nugroho, a spokesman for Indonesia's disaster mitigation agency.

At least 48 people were reported dead in Lampung in southern Sumatra, he said.

With the exact cause of the disaster still unknown, authorities were wary of the risk of a recurrence. Public works minister Basuki Hadimuljono said emergency operations would be carried out continuously but "would stop at the first sign of possible high tides".