The hacking campaign is one of the largest intelligence compromises in US history, with at least eight major companies targeted.
Dozens of nations have been hit by a Chinese hacking campaign, a senior White House official has said.
Carried out by a group dubbed Salt Typhoon, it is one of the largest intelligence compromises in US history.
China hacked at least eight major US telecommunication companies including AT&T, Verizon and Lumen Technologies, resulting in officials in Beijing having access to the private texts and calls of a “large number” of Americans, Washington says.
Now US officials have urged Americans to use encrypted messaging apps to minimise the chances of China intercepting their communications.
But senior White House official Anne Neuberger said authorities don’t believe any classified communications have been compromised.
She added: “We do not believe it’s every cell phone in the country, but we believe it’s potentially a large number of individuals that the Chinese government was focused on.”
Jeff Greene, executive assistant director for cybersecurity at the Cybersecurity and Infrastructure Security Agency said the scope of the compromise is so significant that it was “impossible” for authorities “to predict a time frame on when we’ll have full eviction”.
A separate senior US official declined to provide specific details about the hack but said that China’s access to America’s telecommunications networks was potentially broad and that there was a risk of “ongoing compromise”.
The official said the White House had made tackling the hack a priority and that President Joe Biden had been briefed several times on the intrusions.
On Tuesday, the Chinese embassy in Washington rejected the accusations that it was responsible for the hack.
“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.
Privacy advocates have long supported the use of end-to-end encrypted apps. Signal and WhatsApp automatically implement end-to-end encryption in both calls and messages. Google Messages and iMessage also can encrypt calls and texts end to end.
The hackers accessed three types of information, an FBI official said.