WUHAN -- A total of 59 viral pneumonia cases of unknown cause had been reported in Wuhan, capital of Central China's Hubei province, by Sunday morning, local health authorities said late Sunday.

All the patients have been put in quarantine, with the number in serious condition falling to seven from 11 after treatment and the others in stable condition, the Wuhan Municipal Health Commission said in a statement.

The tests on the exact pathogens and the investigation over the cause of the infections are underway. Influenza, bird flu, adenovirus, SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome) have been ruled out, the statement said.

A preliminary investigation showed that there have been no clear evidence of human-to-human transmission and no reports of infections among medical staff, it said.

Some of the patients, who fell ill with pneumonia between Dec 12-29, are sellers from a local seafood wholesale market that has been temporarily shut down, said the statement.

A total of 163 close contacts have been put under medical observation and they have shown no abnormal symptoms including fever. Local authorities are still searching for more close contacts.