Hong Kong democracy campaigner Joshua Wong returned home Wednesday after being deported from junta-run Thailand, where he was due at events commemorating a massacre of student activists, as he and his supporters blamed China for his detention.

The bespectacled Wong, 19, famed for his galvanising role in the city's 2014 pro-democracy "umbrella movement", was held upon arrival at Bangkok's Suvarnabhumi airport.

"I think Beijing (was) the important factor or motivator for the Thai government to detain me at the airport," Wong told reporters at a press conference late Wednesday in Hong Kong.

He previously said he was stopped by more than 20 police and immigration officers after stepping off the plane in Bangkok at midnight local time and was asked to hand over his passport.

Wong said he was then forced to spend around 12 hours in an airport detention room.

"After they held and kept my passport and refused my request to contact my lawyer and my parents in Hong Kong, I felt hopeless scared and tired," Wong said, adding that Thai authorities told him he was "blacklisted".

Political party Demosisto, co-founded by Wong this year, said it "strongly condemns the Thai government for unreasonably limiting Wong's freedom and right to entry".

Speculation swirled that Thailand's military government was acting under pressure from regional superpower China -- a key ally who has lavished investment and diplomatic support on a junta lacking international friends following its 2014 coup.

Thai student activist Netiwit Chotipatpaisal, who invited Wong to speak in Thailand, said police had told him of a "written letter from the Chinese government to the Thai government concerning this person".

An airport immigration official confirmed there had been an "order" to detain Wong but declined to say who issued it.

But junta spokesman Lietenant General Sansern Kaewkamnerd said: "There had been no instruction or order given, pertaining to Mr Wong."

"Mr Wong had been active in resistance movements against other foreign governments, and that if such actions were taken within Thailand, they could eventually affect Thailand's relations with other nations," the spokesman added.

Netiwit later led a few dozen students wielding umbrellas -- in a nod to Wong's movement in Hong Kong -- in a protest at a Bangkok campus, shouting "Joshua Wong has the right to be here".

Wong has been a perennial thorn in Beijing's side since emerging as an unlikely leader of protests against Chinese political domination of the city.

- 'Lucky' to return -

Last year he was similarly barred from entering Malaysia, where officials sent him back to Hong Kong citing fears his planned talks would damage ties with Beijing.

The Thai military has also busily suppressed its own student pro-democracy protests since its 2014 power grab.

But it would not be the first time the kingdom's junta has appeared to act under pressure from China.

"The Thai military government has kowtowed to China in the past, to Thailand's own detriment," said Thitinan Pongsudhirak, a politics expert at Chulalongkorn University.

He cited Bangkok's deportation of more than 100 Uighurs who had fled China in 2015, a move that drew widespread condemnation from rights groups who say the Muslim minority are heavily repressed by Beijing.

Deporting Wong will "be counterproductive because it will attract global attention," Thitinan said, adding it will "send a signal that Thailand's space is not open".

UN Human Rights Office in Asia spokesman Jeremy Laurence said Wong's detention "raises further concerns about restrictions on peaceful freedom of expression and assembly in Thailand".

Wong had been due to speak at an event in Bangkok on Thursday marking the 40th anniversary of a massacre of pro-democracy students by security forces and royalist militias.

The Thammasat massacre of October 6, 1976, remains a deeply sensitive issue in Thailand's recent history.

Wong's detention also comes almost a year after Hong Kong bookseller Gui Minhai disappeared in Thailand.Gui later resurfaced in China, one of a number of men detained by Chinese authorities over their involvement in the selling of titles critical of Beijing's leaders.

"I'm lucky to have finally returned to Hong Kong, if I couldn't return I can't imagine what sort of situation it would be...I'm lucky I did not become the next person to have disappeared," Wong had earlier said upon arrival in the city Wednesday afternoon.

Wong was among three student leaders convicted in August over the 2014 storming of the forecourt of Hong Kong government headquarters, an event that preceded mass protests that brought much of the city to a standstill for months.

His party Demosisto wants a referendum on Hong Kong's future, including the option of independence.

burs-at/aph