BANGKOK, Nov 20 — Pope Francis arrived in Thailand today to meet with its small but devoted Catholic minority on a seven-day Asian trip that will include a family reunion in Bangkok and take his anti-nuclear message to Japan.

Waiting for a glimpse of the pontiff, excited Catholics thronged around the Vatican's Bangkok embassy and St Louis Hospital to take selfies.

"Once in a lifetime, I want to see him and be able receive prayer from him,” said 60-year-old Orawan Thongjamroon.

The pope's plane touched down outside Bangkok around midday and he descended to a red-carpet airport welcome from church leaders for a visit that coincides with the 350th anniversary of the first papal mission in Siam, the former name of Thailand.

"Dear friends in Thailand and Japan, before we meet, let us pray together that these days may be rich in grace and joy,” read a message on the pontiff's official Twitter account before he left the Vatican.

Catholics are a tiny minority in mostly Buddhist Thailand, accounting for less than 2 per cent of the population.

Pope Francis will meet King Maha Vajiralongkorn, as well as the supreme Buddhist patriarch and Catholic leaders and students before he moves on to Japan on Saturday.

His translator in Thailand will be his cousin and childhood friend, Sister Ana Rosa Sivori, 77, who has worked in Thai schools for more than 50 years. — Reuters