The heads of the FBI and UK domestic security service shared a platform for the first time to issue dire warnings about the threats posed by the Chinese government’s espionage operations, BBC News reports. FBI Director Christopher Wray and MI5 Director General Ken McCallum were speaking at a joint event at MI5’s London headquarters in front of an audience that included business CEOs and senior figures from universities.

“The Chinese government is set on stealing your technology—whatever it is that makes your industry tick—and using it to undercut your business and dominate your market,” the Wall Street Journal reports Wray said in the speech. The FBI director added that the benefits of keeping a piece of technology confidential may sometimes outweigh those of accessing the Chinese market.

“Maintaining a technological edge may do more to increase a company’s value than would partnering with a Chinese company to sell into that huge Chinese market, only to find the Chinese government and your partner stealing and copying your innovation,” Wray said, adding that it represents “an even more serious threat to western businesses than even many sophisticated businesspeople realized.”

In their speech, the two allege that the Chinese government is engaged in a “coordinated campaign” to gain access to important technology, and to “cheat and steal on a massive scale.” They added that the Chinese government’s hacking program dwarfs that of every major country, and that it has a global network of intelligence operatives. The threat means that MI5 is running seven times as many investigations into Chinese activity as it was four years ago, while the FBI is opening roughly two new counterintelligence investigations every day, The Wall Street Journal reports.

“Today is the first time the heads of the FBI and MI5 have shared a public platform,” MI5’s McCallum said. “We’re doing so to send the clearest signal we can on a massive shared challenge: China.” He added that the threat is “real and it’s pressing” and that it could be “the most game-changing challenge we face.”

In terms of specific examples, MI5’s McCallum cited the case of a British aviation expert who was offered a job by a company that was actually a front for Chinese intelligence officers looking to acquire technical information on military aircraft, BBC News reports. Another engineering firm came close to making a deal with a Chinese company, before seeing its technology taken and the deal called off. The incident forced the company into bankruptcy.

A spokesperson for China’s embassy in Washington, Liu Pengyu, denied the allegations, telling the Associated Press in a statement that the country’s government “firmly opposes and combats all forms of cyber-attacks” and “will never encourage, support or condone” them. The Chinese government maintains that it does not interfere in the affairs of other countries, but that it will defend itself against cyberattacks. The statement criticized “U.S. politicians who have been tarnishing China’s image and painting China as a threat with false accusations,” the Wall Street Journal reports.