BRUSSELS, June 22 (AFP) - The EU warned China it would face "very negative consequences" if it presses ahead with a new security law for Hong Kong, stepping up pressure on Beijing over the controversial legislation.

European Commission president Ursula von der Leyen and European Council chief Charles Michel told China's top leaders of their "grave concern" over the new law, which critics say will curb the financial hub's autonomy and freedoms.

The stern message, delivered during a video summit on Monday with Chinese President Xi Jinping and Premier Li Keqiang, adds to a chorus of international concern over Hong Kong, though Beijing has shown no sign of backing down on a law it says is necessary to maintain order.

"We expressed our grave concerns about the proposed national security law for Hong Kong," Michel told reporters after the talks.

"We called on China to follow the promises made to the people of Hong Kong and the international community regarding Hong Kong's high degree of autonomy and guaranteed freedoms."

In response to the EU comments, China's foreign ministry said Tuesday that matters relating to Hong Kong were a "domestic affair".

"We oppose any foreign interference in this matter," ministry spokesman Wang Lutong told reporters at a briefing, saying that Chinese leaders had "expressed our position" at the video summit.

A report of the summit by China's state news agency Xinhua made no mention of Hong Kong but said Xi had stressed his country wanted "peace without hegemony".

Foreign ministers from the G7 group of industrialised nations last week urged Beijing to reconsider the proposed law, which has raised concerns it will end Hong Kong's relative freedoms and open the door to the kind of repression seen in mainland China.

Echoing the language of the G7 statement, von der Leyen said they had made it clear to the Chinese that the EU believes the imposition of the national security law breaches Beijing's international commitments.