The man, an ex-convict identified as Wang Ganggang, was arrested on 3 November in Hebei province's Cangzhou city during a routine police inspection of entertainment venues, the official Xinhua news agency reported on Friday.
"It's at least 65 (victims)," Shi Guizhong, director of the Hebei Public Security Bureau's propaganda division said.
"Even though the case was cracked in Hebei, it involves several provinces, so it's up to the Ministry of Public Security to release information," Shi said, refusing to provide more details.
Police arrested Wang because he appeared suspicious, but later realised he was wanted for homicides in four provinces.
Wang, who used several pseudonyms, including Yang Zhiya, had also seriously injured four other people.
A police officer who works in the Hebei Public Security Bureau said it could be the biggest murder case in recent Chinese history.
Most of the victims were farmers, he said, adding that the case was still being investigated.
Wang had been sentenced to prison and to reform-through-labour camps for robberies and rape, the agency said, quoting media reports.
"His girlfriend broke up with him because of this and as a result, Yang Zhiya developed a vengeful attitude towards society and committed the crimes," it said, quoting the Yanzhao Dushi newspaper.
"Yang Zhiya developed a vengeful attitude towards society and committed the crimes"
Yanzhao Dushi newspaper
He was "extremely cruel" in his methods, usually leaving no witness alive to tell.
Wang later fled north to Hebei where he carried out additional murders, including in the city of Shijiazhuang, where he killed two people. Shijiazhuang is located only about three hours drive from Beijing.
Mass murders are rare in China, but they and other violent crimes are becoming increasingly common.
Earlier this month, state media reported a couple had been arrested in southern China's Shenzhen city in connection with the robbery and murders of 12 women who were lured to their deaths with the promise of a job.
On Friday police said a Chinese man had confessed to raping at least 37 elderly women, some of them in their 90s, because they "are easy to control".