A top White House official on Wednesday said at least eight US telecom firms and dozens of nations have been impacted by a Chinese hacking campaign.

Deputy national security adviser Anne Neuberger offered the new details about the breadth of the sprawling Chinese hacking campaign that gave officials in Beijing access to private texts and phone conversations of an unknown number of Americans.

Ms Neuberger divulged the scope of the hack a day after the FBI and the Cybersecurity and Infrastructure Security Agency issued guidance intended to help root out the hackers and prevent similar cyberespionage in the future.

White House officials cautioned that number of telecommunication firms and countries impacted could still grow.

“We don’t believe any classified communications has been compromised,” Ms Neuberger added during a call with reporters.

She added that Mr Biden has been briefed on the findings and that the White House “has made it a priority for the federal government to do everything it can to get to the bottom of this”.

The Chinese embassy in Washington on Tuesday rejected the accusations that it was responsible for the hack after the US federal authorities issued new guidance.

“The US needs to stop its own cyberattacks against other countries and refrain from using cyber security to smear and slander China,” embassy spokesperson Liu Pengyu said.

The embassy did not immediately respond to messages on Wednesday.