By Tuesday, the virus had killed 20 children, most under the age of two. There had been 1,520 cases reported so far, Xinhua said, a jump of about 600 from the figure released on Monday.
"The current outbreak may be just a beginning," the Ministry of Health's Health News newspaper said. "We cannot exlude the possibility that the virus will spread further."
The Beijing News said that the virus had spread to neighbouring Henan province.
Enteroviruses spread mostly through contact with infected blisters or faeces and can cause high fever, paralysis and swelling of the brain or its lining.
"Most parents, doctors and government officials treat this virus as a normal illness and lose time in discovering and curing it," the Beijing news said.
The delay of reporting the virus to the public by over 40 days has triggered heated discussion and criticism in Chinese media, which said local government officials should be sacked.
China's reported cases of hand, foot and mouth disease in the first four months this year has increased by about 300 percent the same time last year, the Health News newspaper said.
There is no vaccine or antiviral agent available to treat or prevent the virus. Instead, treatment focuses on managing its complications, which can include meningitis and heart failure, the World Health Organisation's acting China Representative, Cris Tunon, said in a statement. (Reporting by Beijing newsroom; Editing by Nick Macfie and Sanjeev Miglani)