A group of men has forced open a door at the Chinese consulate in the city of Houston and entered the diplomatic mission shortly after staff there vacated the building on the orders of the United States government.

The closure of China’s Houston consulate on Friday marks a sharp deterioration in relations between the world’s two biggest economies, with China retaliating by ordering the shutdown of the US mission in the southwestern city of Chengdu.

The 72-hour deadline for the Houston mission’s closure ended at 4pm local time on Friday, and Chinese officials were seen loading large sacks of objects and documents onto U-Haul trucks and tossing more into Dumpster bins.

They were jeered on by a small group of protesters who carried flags expressing support for US President Donald Trump.

Shortly after the last of the Beijing diplomats departed, law enforcement officials cordoned off the area and men who appeared to be US officials pried open a rear door. Then, two uniformed members of the US State Department’s Bureau of Diplomatic Security arrived to guard the door.

Neither the men nor the security officials answered reporters’ questions.

Einar Tangen, political analyst and adviser to the Chinese government, called the US officials’ entry into the Houston consulate “highly unusual” and “against diplomatic protocol”.

“There are now concerns that perhaps this is a ‘Trojan Horse’ situation where they go in and try to find incriminating documents that they will use as a political campaign to vilify China,” he told Al Jazeera from Beijing.

US Secretary of State Mike Pompeo had called the Houston consulate a “hub of spying and intellectual property theft” on Thursday – a claim Chinese officials dismissed as “malicious slander”.

Beijing then ordered the US’s Chengdu consulate shut, saying the move was a “legitimate and necessary response to the unreasonable measures” by Washington.

Foreign ministry spokesman Wang Wenbin later told reporters that some US staff in the Chengdu consulate “were engaged in activities outside of their capacity, interfered in China’s internal affairs, and endangered China’s security and interests”.

He did not say how.

The tit-for-tat moves came as ties between Washington and Beijing deteriorate to what experts say is their lowest level in decades. The two nations are at loggerheads over issues ranging from trade and technology to the new coronavirus pandemic, China’s territorial claims in the South China Sea and its clampdown on Hong Kong.

On Saturday, dozens of police officers were stationed in front of the US mission in Chengdu and staff could be seen pushing trolleys as several consulate vehicles came and went. The US mission has until 10am on Monday to vacate the building, according to the editor of China’s Global Times tabloid.

Al Jazeera’s Katrina Yu, reporting from Chengdu, said people in the city “have been quite supportive of the order to close the consulate here, saying they support Beijing taking a strong stance at what they consider unjustified moves by the US”.

“Yesterday, there was a man who came and quite cheekily set off firecrackers in front of the building in celebration. He was arrested but on Chinese social media, he was hailed as some sort of a hero.”

Amid the deepening spat, the US Department of Justice has pressed charges of visa fraud against four Chinese scientists working in the country, accusing them of hiding their ties to China’s People’s Liberation Army.

The department also said a Singaporean man had pleaded guilty to using his political consultancy in the US as a front to collect information for Chinese intelligence.

Meanwhile, in a major policy speech in California on Thursday, US Secretary of State Mike Pompeo called on “free nations” to triumph over the threat of what he said was a “new tyranny” from China.

“Today, China is increasingly authoritarian at home, and more aggressive in its hostility to freedom everywhere else,” Pompeo said.

“If the free world doesn’t change Communist China, Communist China will change us,” he said.

The speech drew sharp criticism from Beijing, with Hua Chunying, spokeswoman for the Chinese foreign ministry, saying Pompeo’s remarks suggested he wants to “launch a new crusade against China in a globalized world”.

“What he is doing is as futile as an ant trying to shake a tree,” she wrote on Twitter. “It’s about time that all peace-loving people in the world stepped forward to prevent him from doing the world more harm.”

SOURCE: AL JAZEERA AND NEWS AGENCIES