China, along with Russia and Iran, has fuelled a dramatic rise in the threats to the UK from foreign states, according to Ken McCallum.

The number of individuals being investigated for involvement in "state threat activity" had increased by 35 percent in the last year, he said.

He added that agents were "routinely" uncovering plots from foreign states to carry out surveillance, sabotage, arson or acts of physical violence in the UK.

In a speech at MI5's London headquarters, the service's director general also highlighted the "harassment and intimidation of opponents", including pro-democracy activists.

Asked whether China was a national security threat, McCallum said: "Question one is: do Chinese state actors present a UK national security threat?

"And the answer is, of course, yes they do, every day."

McCallum revealed that MI5 had launched an operation to foil a foreign threat in recent days.

"We've intervened operationally again just in the last week" against a "threat which connects back to China", he said.

His warnings come amid a row over the collapse of legal proceedings against two men accused of spying for China.

Beijing has firmly denied the spying accusations as "a total fabrication" and "a vile slander", adding that "China never interferes in other countries' internal affairs".

"The so-called testimony released by the British side after the prosecution withdrew the case is filled with all sorts of groundless accusations against China," a Chinese embassy spokesperson said.

British Prime Minister Keir Starmer's government has faced accusations of killing the case to protect relations with China.

Late Wednesday, the government published three statements it had provided to the Crown Prosecution Service to back the case against the two men.

Multiple Western nations accuse Beijing of using espionage to gather technological information.

They have also accused hacking groups backed by China of a global campaign of online surveillance targeting critics.

The United States, Britain and New Zealand in March 2024 accused Beijing-backed hackers of orchestrating a series of attacks against lawmakers and key democratic institutions -- allegations that prompted angry Chinese denials.