World Bulletin / News Desk
An immigration official, who declined to be named as he was not authorized to talk to media, told Anadolu Agency by phone that Wong was detained shortly after arriving at Suvarnabhumi airport.
"We can confirm that Joshua Wong was barred from entering the country," the official said.
He said he was not allowed to go into details about the detention.
Wong's political party released a statement on Facebook condemning the detention and calling on Hong Kong authorities to ensure he makes it back to the country safely.
It quoted Netiwit Chotipatpaisal, a Thai student-activist expected to meet Wong in Bangkok, as saying that Thai authorities had earlier received a letter from the Chinese government regarding Wong’s visit.
It added Chotipatpaisal's request to see Wong -- "who is still in custody" -- has also been declined.
Wong was due to give a speech later Wednesday at Bangkok's prestigious Chulalongkorn University on the 40th anniversary of a Thai army crackdown on student protesters.
The 19-year-old was at the center of mass 2014 demonstrations against Chinese influence in Hong Kong which came to be known as the Umbrella Movement
The protests brought parts of the territory to a standstill for nearly three months.