The new cases were identified in the cities of Wuhan, Beijing and Shenzhen.
The total number of confirmed cases now exceeds 200, and three have died from the respiratory illness.
The World Health Organization (WHO) said the number of cases rose because of "increased searching and testing".
The new coronavirus strain first appeared in Wuhan in December and has already spread abroad, with two cases in Thailand and one in Japan.
Experts in the UK told the BBC the number of people infected could still be far greater than official figures suggest.
Authorities in the central Chinese city of Wuhan said 136 new cases had been confirmed over the weekend, and a third person there died from the virus.
As of late Sunday, officials said 170 people in Wuhan were still being treated in hospital, including nine in critical condition.
Health officials in Beijing's Daxing district said two people who had travelled to Wuhan were treated for pneumonia linked to the virus.
In Shenzhen, officials said a 66-year-old man showed symptoms of the virus following a trip to visit relatives in Wuhan.
The WHO said "increased searching and testing for [the virus] among people sick with respiratory illness" had led to the jump in confirmed cases.
It said an "animal source seems the most likely source" of the virus, while there was "some limited human-to-human transmission occurring between close contacts."
It added that people could reduce the risk of catching the coronavirus by taking measures such as avoiding "unprotected" contact with live animals, thoroughly cooking meat and eggs, and avoiding close contact with anyone with colds or flu-like symptoms.