Hackers had already been able to gain control of devices such as safes and heating controls, and take over the computer systems of automobiles and aeroplanes, he said.
"China is taking the lead in putting intelligence into devices, from refrigerators to smart thermostats, and this is our weakest link in cyber-security," he said in Beijing.
"I am hoping that in the short time I am here I can raise a warning flag that we have to take security of these devices even more importantly than our large computers or our smart phones," he told a conference of internet security professionals.
"Because there are so many more of these devices, and the more that are connected, then the higher the risk of a potential hack becomes."
McAfee, 70, is the colourful founder of an antivirus software company who once fled Belize after police sought to question him in a murder case.
He has since returned to the United States, where he announced he was running for president.
He amassed an estimated $100 million fortune during the early days of the Internet in the 1990s, but lost most of it to bad investments and the financial crisis.
He was living with a 17-year-old girl in Belize when police came looking for him to discuss the killing of his neighbour - a crime of which he maintains his innocence. He was briefly incarcerated and fled the Central American country.
McAfee's at times dire and alarming speech in Beijing came as his new company MGT Capital prepares to launch cyber-security products later this year.
"Our species has never before faced a threat of this magnitude. And we have not noticed it by and large," he said.
"You may thinking I am exaggerating, that I am an alarmist. I am friends with many of the hackers who have the capability to do enormous damage if they so chose."
Chinese companies such as Xiaomi have been praised for innovation in adding internet connectivity to a variety of devices including air purifiers and rice cookers, allowing users to switch them on from work or on their way home.
Such connections create serious new weaknesses that could leave users' networks especially vulnerable to hacking, McAfee said.
But in a briefing with reporters he also commended Beijing's protection of its domestic internet, which is heavily censored and blocks many foreign websites, for its seeming security against the large-scale breaches seen recently in the US.
"You may notice that last year America suffered hundreds of major hacks from all around the world," he said, and added that he had "heard nothing" of similar hacks on China.
"Now perhaps that's the government's control of the press, I don't know," he said. "But I do know that within certain industries of China, the awareness of cyber-security threats is far greater than our awareness in America."