HONG KONG (AFP) - A Chinese official warned on Thursday of possible "disastrous results" if Hong Kong adopts a foreign electoral system as it mulls political reform, according to a report.

Changes to the political system are a highly charged issue in the semi-autonomous southern Chinese city, regularly sparking protests in favour of greater democracy.

China has promised the former British colony it will be able to elect its next leader in 2017, but has ruled out demands that voters should be able to choose which candidates can stand for the post.

Zhang Dejiang, chairman of China's National People's Congress, reiterated in Beijing that the southern city must carry out democratic reform based on its own laws, according to a Hong Kong delegate also attending the annual NPC session in the Chinese capital.

"You can't just import (electoral systems) or copy foreign countries, or else it may not be a good fit with the local environment and easily enter a democratic trap," the delegate, Ma Fung-kwok, quoted Zhang as saying.

Ma's comments to Hong Kong reporters were screened on Cable TV in the southern city.

"It could bring disastrous results," Zhang was quoted as saying, adding that any democratic reform should be developed in a practical Hong Kong context.

China's official Xinhua news agency quoted Zhang only as saying that Hong Kong and Macau "must observe regulations of the Constitution and the Basic Laws in seeking democracy".

The Basic Law is Hong Kong's mini-constitution.

Many pro-democrats fear that China will control the choice of candidates to secure the election of a sympathetic chief executive.

On Jan 1 an estimated 30,000 demonstrators marched through the city to demand a greater say in choosing future leaders.

Currently the chief executive is elected by a 1,200-strong pro-Beijing committee.

Hong Kong returned to China in 1997 under an agreement with Britain that grants it semi-autonomous status and enshrines civil liberties not seen in mainland China.