Thousands of slogan-chanting Taiwan residents rallied late Wednesday to support the growing pro-democracy demonstrations in Hong Kong, with one saying the city faces a "life-and-death" moment.

The crowd, many of them Hong Kong students studying in Taiwan universities, raised their fists and sang "Boundless Oceans, Vast Skies", a song by the 1980s Hong Kong band Beyond which has become a theme tune of the protests.

Protesters demanded China immediately halt what they called its suppressive policies towards Hong Kong, and honour its commitment of Hong Kong being ruled by Hong Kong people.

Demonstrators also called for Hong Kong leader Leung Chun-ying to step down to shoulder responsibility for the police use of tear gas against crowds.

Demands for unfettered democracy have sparked the biggest civil unrest in Hong Kong for decades.

"I feel I have to stand up as Hong Kong is now moving to a life-and-death moment," Lun Hon Wing, a Hong Kong student from the National Sun Yat-sen University in Taiwan, told AFP.

He and his friend each held up high a yellow umbrella, a symbol of Hong Kong's protests.

Organisers put the turnout at 4,000 but no police estimate was available.

Among the big names at the rally was Wu'er Kaixi, one of the most wanted student leaders from China's 1989 Tiananmen Square protests. He fled to Taiwan after the bloody Chinese army crackdown.

"'One country, two systems' was already dead for some time. Only the name exists: again what the Chinese communists are doing show they are liars," he told AFP.

Taiwan's President Ma Ying-jeou said Monday the protesters' call for free elections had his full backing.

Ma's administration watches events in Hong Kong closely as China wants Taiwan to reunite with it under a "one country, two systems" deal similar to Hong Kong.

The deal, agreed when former colonial power Britain handed Hong Kong back to China in 1997, grants civil liberties not seen on the mainland, including freedom of speech and the right to protest.

China and Taiwan split in 1949 at the end of a civil war.

In Singapore a crowd of around 80 people attended a candlelight vigil in support of the Hong Kong demonstrators.

The hour-long event was held at Hong Lim Park, the only area where protests are allowed in the tightly-controlled city-state.

Organisers set up a mini-shrine for a poster of the "Goddess of Democracy" once displayed in Tiananmen Square, lighting candles around it. Yellow ribbons which have become a symbol of Hong Kong's "Umbrella Revolution" were also given out to participants.

"We felt it was important to show our solidarity with the movement in Hong Kong, " Singaporean human rights activist Rachel Zeng, one of the organisers, told AFP.

"The people of Hong Kong should be allowed to pick a leader who fully represents them, not just someone picked by China," she said.