THIS is the moment a giant tsunami crashed ashore in Sri Lanka unleashing millions of gallons of water that swept thousands to their death in the world's worst natural disaster.

The dramatic satellite pictures show the precise moment a giant wave hit the coastline of Kalutara, Sri Lanka.

Seconds earlier, holidaymakers had watched in stunned horror as the ocean itself was sucked out to sea as the huge wall of water approached, creating a massive vacuum.

As a worldwide aid operation swung into action last night, officials throughout Asia admitted they had almost given up hope of finding anyone alive. The official estimate of 100,000 dead is now expected to be woefully optimistic.

The United Nations said as many as 80,000 people had died in the Indonesian province of Aceh alone, 40,000 of them in just one town.

An area around the town of Meulaboh - a fishing village of 40,000 residents - bore the brunt of the earthquake, which sent massive tidal waves thundering across the Indian Ocean, wreaking havoc in a dozen countries.

And although the official British death toll stood at 50 last night, the Foreign Office was bracing itself for more bad news. Communications with the disaster-hit region are so bad that no one knows how many UK holidaymakers are still missing.

Embassy officials in the Thai island of Phuket admitted the total could still rise steeply in the coming days.

Websites have been inundated with appeals for information from worried friends and relatives of those who have been missing since the tsunami struck on Boxing Day.

The emergency helpline bureau handling calls from those concerned about their loved ones has been receiving around 40,000 calls a day. At its peak, it received in excess of 17,000 calls an hour.

Meanwhile, details continued to emerge of Britons who were caught up in the disaster across Asia.

Among those feared to have been killed is conservationist Lisa Jones, who was working on the tiny Thai island of Koh Phra Thong when the giant tsunami hit.

Fashion photographer Simon Atlee is also believed to be missing after being swept away while on a surprise holiday with his supermodel girlfriend in Thailand. The 33-year-old and his partner, Petra Nemcova, 25, were staying in a beachfront bungalow in the Thai resort of Ko Lak.

Jonathan Hughes, 33, from Leeds, who had been staying at the Charlie Beach Hotel on Koh Phi Phi Don, is also missing.

The bodies of 84 Westerners have been recovered in Thailand but, as yet, no one has been able to establish their nationality.

In Berlin, a grim-faced German Chancellor Gerhard Schroeder cancelled his holiday to warn the death toll would be much higher. He said that about 1,000 Germans were missing.

In Scandinavia, Government officials said more than 2,000 people were unaccounted for.

They were among thousands of Western and Asian holidaymakers packing hotels and bungalows during the height of the tourist season when killer waves struck.

Meanwhile, widespread looting was taking place in Phuket, Phi Phi Island and the nearby province of Phang Nga.

Nine people were arrested for stealing in disaster-hit areas and that thieves were pilfering valuables left behind in abandoned hotels.

An international airlift also begun, with jets from France and Australia carrying critical aid and medical supplies the first to arrive in Phuket.