A 59-year-old Thai woman with dementia who left home eight months ago to see her son nearby, only to apparently walk 640 kilometres into China, arrived back in the kingdom Friday.

Kaeomanee Arjaw, who is from the ethnic Akha hill-tribe, was reported missing on June 12 from her house in the Thai province of Chiang Rai, part of the mountainous "Golden Triangle" zone which borders Laos and Myanmar.

She was found in the southern Chinese city of Kunming in late January carrying a Thai identity card, helping officials swiftly contact the local consulate.

China borders both Laos and Myanmar and it was not immediately clear which route she took across the remote frontiers or how long her journey took.

"She told officials she went there by foot, she kept walking, asking for food from stalls along the way," Colonel Aekkorn Butsabarbodin, of Chiang Rai immigration police told AFP.

On Thursday Kaeomanee's daughter Suchada, 35, flew with Thai officials to Kunming where the pair were filmed clasping each other - the daughter on her knees, sobbing with relief - in an emotional reunion.

In the footage, an official asks the woman where she was going when she left her daughter's home last June.

"I went to see my son... I met him, then I kept walking," the woman answers. "There were no cars around."

She had lost 20 kilograms along her journey, her jubilant daughter added.

Kaeomanee and her daughter flew back to Chiang Rai on Friday.