Sixteen Britons killed by quake
Nine died in Thailand, four in Sri Lanka and three in the Maldives, said the Foreign Office. They have not been named, as relatives are being informed.
BBC correspondent Paul Adams warned there was "every likelihood that figure would rise".
More than 50,000 people are reported dead across the region altogether.
A planeload of supplies from the UK government, including plastic sheeting and tents, arrived in Sri Lanka overnight on Monday.
Further emergency aid supplies worth £100,000 are due to be flown to Asia from the UK as part of a massive humanitarian relief effort.