Beijing has used a coded message for war to warn Washington to 'stop meddling in Hong Kong's internal affairs' after the US Senate passed a bill to support the city's anti-government protests.

The representative office of China's Foreign Ministry in Hong Kong today said 'Don't say we didn't warn you!' - which is a diplomatic term usually reserved by Beijing to signal the start of an armed warfare.

It added that American politicians were 'the enemy of all Chinese people'.

This is the second time China has issued this warning to the United States within six months as tensions between the two nations continue to grow.

China has urged the United States to 'stop meddling in Hong Kong's internal affairs' after the US Senate yesterday unanimously adopted Hong Kong Human Rights and Democracy Act. Pictured, demonstrators hold placards and the US flag on October 14 to support the act

Beijing today told Washington 'Don't say we didn't warn you!' and claimed that American politicians were 'the enemy of all Chinese people'. Pictured, protesters hold British and American flags and a sign reading 'Save Us' near Hong Kong Polytechnic University on Monday

The act would require the US president to annually review the favorable trade status that Washington grants to Hong Kong. Pictured, protesters spill out onto the road during a rally at Chater Garden in Hong Kong's Central during a rally to support the act on October 14

Beijing vowed to take 'effective retaliation' against Washington if the US Congress and President Donald Trump sign off the bill, which backs 'human rights and democracy' in the Chinese-ruled city and threatens to revoke its special economic status.

The US Senate yesterday unanimously adopted the legislation, called Hong Kong Human Rights and Democracy Act.

The act would require the US president to annually review the favorable trade status that Washington grants to Hong Kong.

It also mandates sanctions against Hong Kong and Chinese officials who commit human rights abuses including 'extrajudicial rendition'.

The bill will need to be passed by the Congress before going to Donald Trump.

The act was passed by the US senate as tensions in the Asian financial capital erupted to an unprecedented level this week. Pictured, medical staff help a protester leave Hong Kong Polytechnic University today, on the fourth day of a stand-off with police in Hong Kong

A Fire Services Department diver inspects a drain suspected of having being used by protesters to escape Polytechnic University of Hong Kong besieged by police in Hong Kong

The American lawmakers also approved a measure that would ban the sale of tear gas, rubber bullets and other equipment that have been used by security forces to suppress pro-democracy protests for nearly six months.

Chinese vice foreign minister Ma Zhaoxu immediately summoned the acting US charge d'affaires, William Klein, to lodge a 'strong protest' and demand that the US prevent the bill from becoming law. US ambassador Terry Branstad was out of the country.

'Otherwise, the Chinese side will take strong measures to resolutely counter it, and the US side must bear all the consequences,' Mr Ma was quoted saying by a statement from the Chinese Foreign Ministry.

A US embassy spokesman said Klein 'relayed that we are watching the situation in Hong Kong with grave concern' during the foreign ministry meeting.

The act will need to pass the US Congress before going to President Trump for his approval

China has repeatedly accused the United States of masterminding the unrest in Hong Kong. Pictured, a protester wears a mask depicting Trump during a Halloween march on October 31

The office of the Commissioner of the Ministry of Foreign Affairs of China in Hong Kong urged the US to stop interfering in its domestic affairs 'before it is too late'.

'Don't say we didn't warn you!': Beijing's most severe diplomatic warning The phrase 'Don't say we didn't warn you!' is often used by Chinese Communist Party leaders in the lead up to military conflicts. It was famously used by Chairman Mao in 1949 during the Chinese civil war when he warned his enemies to leave Beiping, now known as Beijing, and surrender to the Community Party. It also appeared in People's Daily columns in 1962 before China went to war with India over a disputed Himalayan border region as well as before the brief Sino-Vietnamese War in 1979. In April last year, China's Xinhua News Agency also used the phrase to caution Washington after it announced plans for imposing tariffs on about 1,300 Chinese products following an investigation into the Chinese foreign trade policies. 'Anyone who is familiar with Chinese diplomacy would know the weight of this sentence,' a commentary at the time said. Advertisement

'Otherwise [the United State] will certainly become the victim of its own evil deeds. Don't say we didn't warn you!' A spokesperson of the Commissioner said in a statement.

China last time used the diplomatic term to warn the US in May during tensions sparked by the trade war.

People's Daily, the mouthpiece of the Communist Party, sent out the message to hint that Beijing would ban exports of 'rare earth' minerals to the US.

The spokesperson claimed that the unrest in Hong Kong 'is by no means about human rights and democratic problems', adding that 'anti-China individuals are using violent measures in a bid to overthrow a legitimate regime and "one country, two systems".'

The statement also accused the US of 'supporting terrorism' and threatening peacekeepers.

'American politicians are the enemy of all Chinese people, including our compatriots in Hong Kong,' it said before adding that Washington cannot deny being a 'black hand' behind the chaos.

China had also reacted angrily when the US House of Representatives passed a similar measure last month.

The American lawmakers also approved a measure that would ban the sale of tear gas, rubber bullets and other equipment that have been used by security forces to suppress protests for nearly six months. Pictured, protesters react as police fire tear gas during a rally on Monday

Chinese vice foreign minister Ma Zhaoxu (pictured in April) immediately summoned the acting US charge d'affaires, William Klein, to lodge a 'strong protest' against the US legislation

The Senate 'sent a clear message to Hong Kongers fighting for their long-cherished freedoms: We hear you, we continue to stand with you and we will not stand idly by as Beijing undermines your autonomy,' Republican Senator Marco Rubio said.

Passage of the bill marks 'an important step in holding accountable those Chinese and Hong Kong government officials responsible for Hong Kong's eroding autonomy and human rights violations'.

The Senate Foreign Relations Committee's top Democrat, Robert Menendez, added that the legislation 'makes it clear that the US will stand firmly and unambiguously with the legitimate aspirations of the people of Hong Kong.'

Chinese foreign ministry spokesman Geng Shuang said the US purpose was to 'support the extremists and violent elements against China that are trying to mess up Hong Kong... and realise their sinister plot to hinder China's development by taking advantage of the Hong Kong issue.'

Hong Kong has been rocked by anti-government protests since the beginning of June

The pro-democracy movement was ignited in June when millions took to streets in opposition to a now-abandoned attempt to allow extraditions from Hong Kong to the mainland.

The protests and resulting crackdowns have turned parts of Hong Kong into violent battlegrounds for weeks.

On Tuesday protesters occupying a university defied warnings to surrender, as skirmishes between police and demonstrators continued.

The Senate bill updates the original Hong Kong Policy Act of 1992.

Senator Ben Cardin noted how Hong Kong had enjoyed a special economic status for years, one that relied on authorities 'protecting democracy and human rights' in the territory.

'That was the commitment. And if they don't comply with that, the special status should no longer be available,' Cardin said.

The US House and Senate will now harmonise the texts into a single bill to pass the Congress and go to Donald Trump's desk for his signature.