The US ordered China to shut its consulate in Houston as a message to Beijing to reel in its operations to steal US science and technology secrets, a senior State Department official said Friday. "There comes a time when you have to say, enough is enough," said the official, who insisted on anonymity.

Beijing has "egregiously abused its free and open access" to US society by running operations to illegally collect US intellectual property, the official said.

"Houston is a firm demonstration that we are serious."

On Tuesday the State Department ordered the consulate in  the largest city in Texas closed, giving Beijing until Friday to complete the process.

Trucks have been arriving day and night to remove possessions and equipment, and on Wednesday plumes of smoke were seen coming from the building, suggesting Chinese officials were burning documents.

Early Friday numerous Chinese officials, all wearing coronavirus masks, were seen loading large bags on to U-Haul trucks and throwing away bags in nearby trash bins.

A Justice Department official told reporters, also on grounds of anonymity, that while the United States expects some efforts at espionage and intellectual property theft from foreign missions, the activities from Houston "went well over the line."

They included directing Chinese students and researchers on what kinds of information and technology to obtain, recruiting Americans to their technology program, and targetting Chinese dissidents residing in the United States.

The public examples of such behavior, known from a series of criminal cases over the past three years, "are merely the tip of the iceberg" of what is known to US intelligence, the Justice official said.

A US intelligence official told reporters that the science and technology "collectors" at the Houston consulate "were particularly aggressive, and successful."

Early Friday, Beijing retaliated by ordering the United States to close its consulate in Chengdu, Sichuan province.