China has reported just a handful of Covid-19 deaths as a wave of Omicron infections has swept the country’s biggest cities, stoking suspicion among public-health experts and relatives of deceased patients that the government isn’t accurately accounting for the impact of the virus.

Despite widespread reports of soaring infections, crowded hospitals and overwhelmed crematoria, Chinese health authorities had by Tuesday reported only seven Covid-related deaths since the country abruptly eased many of its pandemic-control measures more than two weeks ago. Two deaths were reported in Beijing on Monday and five the following day.

But on Wednesday, China’s National Health Commission said there had been no new deaths—and that it was retracting one of the Beijing fatalities from the official tally of Covid’s toll. No explanation was given. China now blames the virus for killing 5,241 of its 1.4 billion people in the past three years.

Chinese health authorities on Tuesday broadcast for the first time their criteria for classifying a death as being Covid-related, saying only fatal cases of pneumonia or respiratory failure linked directly to the coronavirus would qualify.

“Deaths from other illnesses and underlying causes such as cardiovascular disease and heart attack are not classified as Covid-related deaths,” Wang Guiqiang, head of the infectious-disease department at Peking University First Hospital, said at a National Health Commission press briefing.

The best way for the Chinese government to fight the current wave of infections is to be as transparent as possible, public-health experts said.

Photo: alex plavevski/Shutterstock

That definition is unusually narrow by global standards. The Beijing-ruled territory of Hong Kong, for example, defines a Covid-related death as one in which a patient dies within 28 days of first testing positive for the virus, even if the ultimate cause of death isn’t directly related to Covid.

The U.S. Centers for Disease Control and Prevention distinguishes deaths depending on whether Covid is an underlying or a contributing cause, though both are included in the nation’s pandemic toll.

A retiree living in Beijing said his 60-year-old diabetic cousin died suddenly over the weekend, a few days after testing positive for Covid before a scheduled surgery. The hospital listed diabetes as the cause of death, he said.

“[Doctors] told us that the cause of death would always be something else unless you don’t have any underlying diseases and are only hospitalized because of Covid,” he said.

The family found it hard to accept the official verdict of the cause of death, he said, adding that his cousin’s body had to wait in a long line before being cremated.

The Wall Street Journal reported last week that one of Beijing’s designated crematoria for Covid patients was flooded with dead bodies in the days after pandemic restrictions were lifted, though authorities had reported no Covid deaths at the time.

A woman answering a funeral-service hotline in nearby Hebei province said she has recently been fielding many more inquiries than normal, both locally and from people in Beijing.

The National Health Commission didn’t reply to a request for comment about the potential undercounting of deaths.

Mainland China will likely face a death toll of more than 300,000 people by April 1 next year if the country continues on its current path, according to the latest projections from a Covid forecasting model developed by the Institute for Health Metrics and Evaluation at the University of Washington, Seattle.

Deaths in China could rise to nearly 9,000 a day by the end of March without policy changes from Beijing, such as compulsory wearing of masks and stay-at-home orders, said Ali Mokdad, an epidemiologist at the institute. The government could reduce the number of deaths by around 400,000 over the course of the year if it reimposed some of those mandates, he said.

The forecasts take into account population density, vaccine efficacy, demographics and the fatality rate from an earlier Omicron wave in Hong Kong, among other factors, according to Prof. Mokdad. In the spring, Hong Kong recorded what at the time was the world’s highest Covid fatality rate, as the city’s elderly population had almost no exposure to the virus and very low rates of vaccination. Public-health experts warn that China’s sizable over-80 population has a similar lack of immunity to Covid and remains undervaccinated. China’s public-health system also is by some measures less prepared than Hong Kong to handle a surge in infections, they say.

People lining up at a makeshift clinic set up inside a stadium in Beijing.

Photo: ALESSANDRO DIVIGGIANO/REUTERS

The best way for the Chinese government to fight the current wave of infections is to be as transparent as possible, so that people can take proper precautions, public-health experts said.

Reporting accurate death data is difficult for overworked medical workers and needs to be incentivized by the central government, which isn’t happening in China, according to Katherine Mason, a medical anthropologist at Brown University.

“Part of it is probably attributing to other causes and part of it is probably just plain old not reporting because there’s no good that can come out of it for those local officials,” she said.

After three years of casting Covid as a serious health threat, Chinese authorities have recently done an about-face, rolling out waves of messaging that portray Omicron as far less deadly than previous variants.

“They’re trying to back up their assertion that Omicron is not that bad and people might be getting sick but they’re not dying, but I don’t know how long they’re going to be able to keep that up,” Prof. Mason said.

The University of Washington’s Prof. Mokdad called for the donation of vaccines and antiviral medicine to help reduce mortality rates in China partly because of the vital role the country plays in supplying goods, including medical supplies, to the rest of the world.

“China deserves to be supported immediately, right now,” Prof. Mokdad said.

Write to Liyan Qi at Liyan.qi@wsj.com and Cao Li at li.cao@wsj.com