Chinese health officials on Wednesday significantly increased their estimates of the number of cases and deaths in China caused by a new mystery pneumonia that international health officials believe originated here late last year.

Officials in Guangdong Province, the center of China's epidemic, reported an estimated 792 cases and 31 deaths as of the end of February, a rise from the 305 cases and five deaths they had previously reported.

The new tallies mean that China now probably has had more cases and deaths than any other country, although the latest estimates have not been officially approved by China's Ministry of Health or reviewed by international health officials. About 500 cases have been reported elsewhere in the world.

The new figures are being released just days after a World Health Organization team arrived in China to help investigate this country's epidemic of the mystery pneumonia, which goes by the name SARS, for severe acute respiratory syndrome.

For months, Chinese officials tried to hide the problem, health experts said, and in recent weeks world health officials have applied increasing pressure on China to improve its cooperation and statistical reporting on the disease.

While all other countries that have experienced cases of the new pneumonia, including Vietnam, Singapore and Canada, send daily updates of cases and deaths to the World Health Organization, China has been consistently unwilling or unable to provide such information.

Even today's newly revised estimates, which officials of the World Health Organization praised as a ''great step forward,'' cover only cases through the end of February and provide no information about cases in the past four weeks. The previous tallies covered only cases reported up to Feb. 10.

''We want to keep the spotlight on folks here and to encourage them to be part of the solution,'' said Dr. Rob Breiman, of the International Center of Diarrheal Disease Research Bangladesh, who is a member of the W.H.O. team currently in China. ''We want to use the incredible amount of information they have collected here to help solve the problem.''

Meanwhile, in one of the few encouraging developments, many of the first wave of patients in Hanoi, Hong Kong and Singapore are recuperating well enough to expect to go home soon, said Dr. Mark W. A. P. Salter, an expert in infectious diseases at the W.H.O.

The precise number of patients who are ready for discharge or who have been discharged was not available, Dr. Salter said. Some SARS patients have been hospitalized for more than a month.

Doctors do not know precisely when SARS patients can no longer transmit the disease to other people. Information so far from reports of people who have recuperated is that they pose no danger to others.

A clearer picture of the course of SARS emerged on Wednesday after 80 doctors who have treated cases in 13 countries held a teleconference moderated by Dr. Salter.

The participants said that SARS usually begins with high fever, chills muscle aches and a dry cough, and the way it progresses appears consistent in all countries.

After about a week, SARS patients tend to fall into either of two groups.

One group -- an overwhelming majority of patients -- begins to show improvement even without specific therapy.

In a second group, from 10 to 20 percent of patients develop increasing difficulty in breathing. Such patients usually required breathing assistance with a mechanical ventilator, and many have had to stay on ventilators for a long time. Most SARS deaths have involved patients in this group.

Patients 40 and older who have chronic ailments like those affecting the heart, liver, lung and bowel seem to be those who have become sickest. But a vast majority of patients had no known chronic disease before they became ill from SARS.

Officials from the World Health Organization first sat down on Tuesday with their Chinese counterparts to look at the internal data concerning the epidemic and said they were generally impressed with how the Chinese had investigated and sought to control the disease.