Taiwan's president threw his weight behind Hong Kong's democracy protesters on Monday, saying he was "very concerned" by events in the city and urging China to proceed with "peaceful and cautious measures".

Chaotic protests saw Hong Kong police fire tear gas on Sunday at demonstrators enraged by China's refusal to grant full democracy to the semi-autonomous city, with thousands remaining on the streets into Monday.

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

"We fully understand and support Hong Kong people in their call for full universal suffrage," Ma told a gathering of business leaders in Taipei.

"Developments in Hong Kong have drawn the close attention of the world in the past few days. Our government has also been very concerned," he added.

"We urge the mainland authorities to listen to the voice of Hong Kong people and use peaceful and cautious measures to handle these issues."

Ma's administration watches events in Hong Kong closely as Beijing wants Taiwan to reunite with the mainland under a "one country, two systems" deal similar to that through which Hong Kong is ruled.

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.

Ma has sought to boost ties with China since he took office in 2008, but he has rejected reunification under a Hong Kong-style arrangement.

While voicing support for the protesters, he also urged them to refrain from violence, warning that the unrest in the city could send shockwaves through the wider Asian economy.

"Hong Kong is a global financial centre. Any political turbulence may impact on Asia and even the world," Ma said.

"We also call for Hong Kong people to use peaceful and rational methods to highlight their appeal. Any conflict would be the last thing we would like to see."

He spoke as dozens of Taiwanese students chanted slogans and scuffled with police during a protest in support of the Hong Kong demonstrators outside the city's liaison office in Taipei.

The office's director John Leung was booed by Taiwanese students when they asked if he backed the use of force against the protesters and he replied that "conflicts were sometimes unavoidable while handling such big events".

The protests come after Beijing said Hong Kong could hold elections for its next leader in 2017 but would insist on vetting the candidates, with activists deriding this as "fake democracy".

Ma said both Hong Kong and the mainland would benefit from allowing free elections in the city.

"It is generally believed that Hong Kong will be able to move towards democracy step by step," he said.

"It is our belief that it would be a win-win situation for both Hong Kong and the Chinese mainland if universal suffrage could be adopted."