FBI Director Christopher Wray on Wednesday warned that Chinese hackers are preparing to “wreak havoc and cause real-world harm” to the US.

“China’s hackers are positioning on American infrastructure in preparation to wreak havoc and cause real-world harm to American citizens and communities, if or when China decides the time has come to strike,” Wray told the House Select Committee on the Chinese Communist Party.

Though cyber officials have long sounded the alarm about China’s offensive cyber capabilities, Wray’s dramatic public warning underlines the huge level of concern at the top of the US government about the threat Chinese hackers pose to critical infrastructure nationwide. The head of the National Security Agency and other senior US officials are also testifying on Chinese cyber activity in front of the panel Wednesday.

PRC hackers, Wray said, are targeting things like water treatment plants, electrical infrastructure and oil and natural gas pipelines, Wray said. “our water treatment plants, our electrical grid, our oil and natural gas pipelines, our transportation systems.

The Chinese hackers are working “to find and prepare to destroy or degrade the civilian critical infrastructure that keeps us safe and prosperous,” Wray said. “And let’s be clear: Cyber threats to our critical infrastructure represent real world threats to our physical safety.”

The Chinese government has previously denied allegations of hacking efforts.

The hearing comes in the wake of a big push by US and Chinese officials to ease tensions in the relationship between the two superpowers. At a meeting in November, Chinese President Xi Jinping assured US President Joe Biden that China would not interfere in the 2024 US election, CNN exclusively reported on Tuesday. That assurance was reiterated by the Chinese foreign minister to Biden’s national security adviser this past weekend, sources told CNN. US officials will be closely watching to see if Xi keeps his word.

Asked about that assurance, Wray said: “China’s promised a lot of things over the years, so I’ll guess I’ll believe it when I see it.”

“The truth is the Chinese cyber actors have taken advantage of very basic flaws in our technology. We have made it easy on them,” Jen Easterly, who leads the US Cybersecurity and Infrastructure Security Agency, told lawmakers.

“Unfortunately, the technology underpinning our critical infrastructure is inherently insecure because of decades of software developers not being held liable for defective technology. That has led to incentives where features and speed to market have been prioritized against security, leading our nation vulnerable to cyber invasion. That has to stop,” Easterly said.

The FBI and Justice Department have previously stressed their focus on preventing malign campaigns by the Chinese government and hackers.

CNN has reported that in recent months, federal law enforcement has used a court order to allow the Justice Department to remove malicious code from, or otherwise protect hundreds of devices in the US that are at the center of a Chinese hacking campaign targeting sensitive US critical infrastructure. Nevertheless, the hackers are believed to be deeply entrenched in US infrastructure.

The move by the Justice Department and FBI is part of a broader, government-wide attempt to blunt the impact of a persistent Chinese hacking effort that US officials fear could hinder any US military response in the event of a Chinese invasion of Taiwan, CNN has reported. The hackers are believed to be using access to some of the devices to burrow further into sensitive critical infrastructure — things like ports and transportation networks.

Wray said Wednesday that the PRC’s efforts extend beyond technology, his remarks show, warning that “they target our freedoms, reaching inside our borders, across America, to silence, coerce, and threaten our citizens and residents.”

CNN’s Evan Perez contributed to this report.