A member of a radical Hong Kong political opposition party Sunday said he had been arrested six months after throwing a t-shirt at Chinese President Hu Jintao's motorcade.

League of Social Democrats vice-chairman Avery Ng told AFP he had been arrested on Saturday on a charge of public nuisance, after throwing the t-shirt bearing a drawing of the late Chinese dissident Li Wangyang on June 29.

Hu was visiting the former British colony to mark the 15th anniversary of the territory's handover and to preside over the city's leadership change on July 1.

"We were just exercising our basic human right to protest... and that was already being violated by the police," Ng told AFP, saying that he threw his t-shirt because police confiscated demonstrators' banners shortly before the motorcade's arrival.

Police said they had arrested a 35-year-old local man surnamed Ng on Saturday for a count of "nuisance crimes committed in a public place".

Ng was released on bail and will appear in court on Monday.

He said he believed the government was attempting to hush opposition ahead of a mass anti-government protest planned for New Year's Day.

Protesters from various opposition groups plan to take to the streets on January 1 to air concerns over freedom of expression, which they fear is in decline due to increasing Chinese influence on the city, among other issues.

"The whole thing is politically motivated, there's no question about it," Ng told AFP, saying that his arrest would not stop him from attending any future demonstrations.

Police used pepper spray to disperse hundreds of protesters as they chanted anti-Beijing slogans on loudspeakers outside the five star hotel Hu was staying in on June 30.

Around 400,000 people took to the streets the next day to express their opposition to Hong Kong's new chief executive Leung Chun-ying, who was sworn in by Hu, and to express their anger after 15 years of Chinese rule.

A government spokesman declined to respond to Ng's comments, but said: "Anyone can give opinions on various matters and the (Hong Kong) government fully respects the freedom of opinion of every individual."

He added that freedom of expression and speech were "core values".

The right to protest is one of the cherished freedoms enshrined in the "one country, two systems" model that has applied to Hong Kong since its return to Chinese rule in 1997.

The city of seven million people maintains a semi-autonomous status with its own legal and financial system.