The world's first museum dedicated to the Tiananmen Square crackdown opened in Hong Kong Saturday with an emotive ceremony and protests from pro-China demonstrators.

Almost 25 years after the Chinese authorities' brutal repression of pro-democracy protesters in Beijing, the permanent exhibition is one of the only places in China where the massacre of June 3-4, 1989, can be commemorated.

All reference to the crackdown is banned on the mainland, where many remain unaware of it.

"The one thing I remember most vividly was that 25 years ago, right after the massacre, Beijing residents told us one thing -- that we must tell the true story of what happened to the world," said Lee Cheuk-yan, chairman of the pro-democracy group which is funding the museum.

The Alliance in Support of Patriotic Democratic Movements of China also organises the annual June 4 candlelight vigil in Hong Kong attended by tens of thousands.

Lee dedicated the museum to those who sacrificed their lives for democracy.

The opening was disrupted by more than a dozen pro-China placard-wielding protesters who shouted at museum organisers outside the building, calling them "traitors".

"They don't talk about the Nanjing Massacre and only talk about June 4," an angry protester shouted, referring to an incident in which China says more than 300,000 people were slaughtered by Japanese troops during World War II.

The demonstrators, who called themselves the 6.4 Truth group, said the Alliance presented a skewed account of the crackdown and that Chinese troops were also killed during the incident.

However, they did not deter a steady stream of visitors, including people from mainland China, to the museum.

- Painful memories -

"I feel after seeing this, (the view on the incident) will be completely different," Kitty Kau, originally from the mainland and who has been living in Hong Kong for the past 12 years, told reporters.

"There are many people in China that don't know about June 4. Even if they knew about it, they would not talk about it," Kau said.

The 800-square foot (74.32 square-metre) venue, in the commercial district of East Tsim Sha Tsui, features video clips and photographs -- including the famous 'Tank Man' image of a civilian staring down a long row of military vehicles.

There is also a two-metre tall statue of the Goddess of Democracy, similar to one erected at Tiananmen Square during the protests.

"If one day you could open this museum in Beijing, that would mean that the whole incident would be rectified," said Jonathan Chan, who was at Tiananmen Square during the crackdown as a representative of Hong Kong's federation of students, supplying tents and food to protesters.

Positioned at a supply station in the square, he told how he saw protesters, some of them already dead, being brought in with gunshot wounds.

"It was disbelief and anger," Chan said of his feelings as he witnessed the bloodshed, the memory still fresh even after a quarter of a century.

Beijing has never provided an official final toll for the military crackdown, which was condemned worldwide. Independent observers tallied more than 1,000 dead in Beijing.

The Chinese Communist Party branded the Tiananmen protests a "counter-revolutionary rebellion", but pro-democracy advocates in Hong Kong have consistently commemorated the incident.

Every year, tens of thousands of residents gather at the city's Victoria Park to mark its anniversary.

Since returning to Chinese rule in 1997, Hong Kong enjoys a level of civil liberty that is unavailable in China under the so-called "One Country Two Systems", which guarantees the city's semi-autonomous status.