China's foreign affairs office in Hong Kong lashed out against the British government Wednesday over its criticism of the city's new national security law, saying it showed it had a "deep-rooted mindset as a colonizer".

Hong Kong, a former colony of Britain before the 1997 handover back to China, on Tuesday passed a security law punishing five major crimes after a fast-tracked legislative process.

British foreign minister David Cameron said it was a "rushed" process for a law that will "further damage the rights and freedoms enjoyed in the city".

In response, Beijing's foreign affairs commissioner blasted Britain for being "hypocritical and exercising double standards", as it referred to London's own national security laws, including one passed last year.

"The United Kingdom has been making inflammatory and irresponsible comments on Hong Kong's situation... it's all due to the deep-rooted mindset as a colonizer and preacher," it said in a statement Wednesday.

"We urge the UK to set its position right, face the reality, and give up on the fantasy of continuing its colonial influence in Hong Kong."

That statement also drew a rebuke from the Chinese embassy in Britain, which called it "a serious distortion of the facts".

The embassy said the law, which carries penalties of up to life in prison for crimes related to treason and insurrection, "fully safeguards the rights and freedoms enjoyed by Hong Kong residents".

"We urge the UK to cease its baseless accusations... refrain from interfering in China's internal affairs under any pretext," it said.

The United States, United Nations, European Union and Japan have also publicly spoken out against the law.

Beijing's foreign ministry spokesman Lin Jian fired back on Wednesday, stressing that "attacks and smears" against the new Hong Kong law by other governments and outside groups were "doomed to fail".

"The firm determination to oppose any external interference in Hong Kong affairs is unswerving," Lin said.

(AFP)

File photo.

China brands UK 'colonizer' for criticizing Hong Kong security law