Spread the word, the messages said: The Trump administration was about to lock down the entire country.

“They will announce this as soon as they have troops in place to help prevent looters and rioters,” warned one of the messages, which cited a source in the Department of Homeland Security. “He said he got the call last night and was told to pack and be prepared for the call today with his dispatch orders.”…

Since that wave of panic, United States intelligence agencies have assessed that Chinese operatives helped push the messages across platforms, according to six American officials, who spoke on the condition of anonymity to publicly discuss intelligence matters. The amplification techniques are alarming to officials because the disinformation showed up as texts on many Americans’ cellphones, a tactic that several of the officials said they had not seen before.

That has spurred agencies to look at new ways in which China, Russia and other nations are using a range of platforms to spread disinformation during the pandemic, they said.