Kathy Mueller, of the International Federation of Red Cross and Red Crescent Societies, said the toll was likely to rise as conditions became clearer.

“The situation and the death toll will remain fluid over the next days and even weeks,” she said.

Aid workers were helping the injured, taking in clean water and tarpaulins to provide shelter, she said, adding that the group was already preparing for the possibility of diseases breaking out.

Hong Kong’s Immigration Department said it had not yet received calls from residents in need of help. It was also in contact with the Chinese embassy in Indonesia, a spokesman said.

No foreigners have so far been confirmed among the dead.

The tsunami struck less than three months after a huge earthquake struck Palu on the island of Sulawesi killing 2,256 people.

Photographer Oystein Andersen described how he was caught in the disaster while on the beach taking photos of Krakatoa.

“I suddenly saw a big wave,” he wrote on Facebook. “I had to run, as the wave passed the beach and landed 15-20m inland. [The] next wave entered the hotel area where I was staying and downed cars on the road behind it.”

Asep Perangkat said he was with his family when the wave surged through Carita, dragging cars and shipping containers.

“Buildings on the edge of the beach were destroyed. Trees and electric poles fell to the ground.”

In Lampung province, on the other side of the strait, Lutfi Al ­Rasyid fled the beach in Kalianda city, fearing for his life.

“I could not start my motorbike so I left it and I ran... I just prayed and ran as far as I could,” the 23-year-old said.

‘Child of Krakatoa’, the lava bomb-hurling volcano that triggered Indonesia’s latest deadly tsunami

Azki Kurniawan, 16, said he was having vocational training with 30 other students at Patra Comfort Hotel near Carita beach when people suddenly burst into the reception yelling, “Sea water rising!”

He said he was confused because he did not feel an earthquake, but ran to the car park to try to reach his motorbike.

By the time he got there, it was already flooded.

“Suddenly a 1-metre wave hit me,” he said. “I fell down, the water separated me from my bike.

“I was thrown into the fence of a building ... and held onto the fence as strong as I could, trying to resist the water, which feels like it would drag me back into the sea. I cried in fear ... I was afraid I would die.”

Krakatoa, which forms a small island in the Sunda Strait between Java and Sumatra, emerged around 1928 in the ­crater left by Krakatoa, which erupted in 1883 killing at least 36,000 people.

“The cause of the undersea landslide was due to volcanic activity of Anak Krakatoa, which coincided with a high tide due to the full moon,” Nugroho said in Yogyakarta.

Local meteorological authorities said the tsunami’s height was between 28cm and 90cm. A spring tide, caused by the full moon, possibly made the wave larger, they said.

Tsunamis triggered by volcanic eruptions are relatively rare, caused by the sudden displacement of water or “slope failure”, according to the International Tsunami Information Centre.

Unlike those caused by earthquakes, which trigger alert systems, they give authorities very little time to warn residents of the impending threat.

Professor David Rothery of the Open University said the proximity of the volcano to the coast gave authorities almost no warning.

“Tsunami warning buoys are positioned to warn of tsunamis originated by earthquakes at underwater tectonic plate boundaries. Even if there had been such a buoy right next to Anak Krakatoa, this is so close to the affected shorelines that warning time would have been minimal given the high speeds at which tsunami waves travel,” he said.

Igan Sutawijaya, an expert on geological disasters, said the waves might not be directly linked to an eruption.

‘Expect more disasters like Palu’: why giant quakes continue to devastate poorer Asian communities

“My suspicion is that there was a landslide under the sea. Perhaps a trench crumbled,” he said. “It doesn’t make sense that it was caused by the eruption of the Krakatoa.”

Indonesia’s Centre for Volcanology and Geological Hazard Mitigation said the eruption of the 338-metre volcanic mountain was similar to others that had occurred since June 29. Such a tsunami would normally require a huge landslide entering the sea, but none was observed, it said.

Authorities at first said the wave was not a tsunami but a tidal surge and urged people not to panic. Nugroho later apologised, saying because there was no earthquake it had been difficult to ascertain the cause.

“If there is an initial error we’re sorry,” he wrote on Twitter.

The wave swamped parts of the coast around the Sunda Strait, leaving at least 164 people dead in worst-affected Pandeglang district on Java’s western tip.

There were many casualties at two hotels in the area, Nugroho said, without elaborating.

Eleven died further north in Serang, and 48 were killed in South Lampung, on Sumatra.

Heavy equipment was being transported to badly hit areas to search for victims, and public kitchens were being set up.

Hong Kong residents in Indonesia who need help can call the 24-hour hotline of the Hong Kong Immigration Department at (852) 1868.

Agence France-Presse, The Washington Post, Kyodo, Associated Press