Parts of Chiang Mai were bathed in a surreal, magical glow as thousands of lanterns floated up to the sky during the annual Floating Lantern festival in northern Thailand known as Yi Peng, or Yee Peng.

During the festival, taking place at the end of the rainy season and held during a full moon, paper lanterns are released into the air - thought to bring good luck as it symbolises one's troubles floating away.

Yi Peng usually coincides with Loy Krathong, a festival where Thais across the nation set candle-lit floats adrift in rivers, lakes and the sea - a practice said to originate from an ancient ritual paying respects to the water spirits.

The mood in the capital city of Bangkok, however, was less than festive on Monday as mourners marked the end of the first month of a year of official mourning for King Bhumibol Adulyadej, who died on Oct 13.

Yi Peng usually draws tens of thousands of tourists, but locals said they were expecting smaller crowds this year.