The powerful quake generated waves 36ft (11m) high in some areas
The child of a British couple is missing presumed dead after a tsunami hit the South Pacific island of Samoa, the Foreign Office (FO) has said.
The two-year-old's parents were receiving consular assistance at the New Zealand High Commission, Samoa's British Honorary Consulate said.
A spokesman for the British High Commission in New Zealand said the missing boy was a New Zealand citizen.
The tsunami killed more than 100 people in Samoa, American Samoa and Tonga.
Regional tsunami warnings have also been issued in Indonesia after a strong earthquake with a 7.9 magnitude struck off the coast of Sumatra.
British Honorary Consulate Dr Stephen Rogers, based in Apia in the north of the island, said there were no other reports of UK casualties.
"We have a number of British people who have lost all their possessions," he said.
"We've also had calls from a number of Brits in different accommodation who are claiming to be okay. We've had calls from the UK about people we've got no information about."
About 20 Britons are thought to have been on Samoa at the time the tsunami struck.
Dr Rogers said the initial quake shook the entire island and damaged buildings, but added that the devastation was largely confined to the south east.
He said 36ft (11m) waves swept inshore about half an hour after the quake, washing away anything in its path, including roads and houses.
He also said he managed to pick up five Britons in their 20s and 30s - including three tourists.
Prime Minister Gordon Brown has sent his "heartfelt condolences" to the people of Samoa, Tonga and the Philippines .
He said: "All of us watching these scenes will be shocked and saddened at the sheer scale of the devastation. We stand ready to help in any way we can".
The tremor, with a magnitude of between 8 and 8.3, struck about 120 miles from American Samoa.
Samoan officials say whole villages have been destroyed with thousands reportedly left homeless in American Samoa.
The Foreign Office has advised against all but essential travel to Samoa and Tonga until further notice.