Young Hong Kong democracy activist Joshua Wong appeared to have foreseen his trip to Bangkok would not be smooth, according his Facebook.

Mr Wong wrote on his Facebook page at Hong Kong international airport Tuesday night that he would be in Bangkok for four days for his speeches at Chulalongkorn and Thammasat universities.

He intended to share his experiences in his pro-democracy "umbrella movement" in Hong Kong in 2014, as well as elections there, and to exchange opinions with local parties.

He wrote that he had concerns about the trip to Bangkok because his entry to Malaysia had been denied in May last year. At that time, he was invited to talk about democracy in China but was forced to fly back to Hong Kong for his alleged threat to security and bilateral relations.

His planned speeches in Bangkok were scheduled to commemorate the 40th anniversary of the Oct 6, 1976 massacre on students who were protesting at Thammasat University against the return of former military dictator Field Marshal Thanom Kittikachorn.

Late Wednesday morning, Mr Wong was reportedly detained by immigration police at Suvarnabhumi airport pending his flight back to Hong Kong.