BEIJING — China acknowledged Friday that the coronavirus death toll in the one-time epicenter city of Wuhan was nearly 50 percent higher than reported, underscoring just how seriously the official numbers of infections and deaths around the world may be understating the dimensions of the disaster.

“We are probably only seeing the tip of the iceberg,” said Barcelona University epidemiologist Antoni Trilla, who heads the Spanish government’s expert panel on the crisis.

Worldwide, the outbreak has infected more than 2.1 million people and killed over 145,000, according to a Johns Hopkins University tally based on figures supplied by government health authorities around the globe. The death toll in the U.S. topped 33,000, with more than 670,000 confirmed infections.

Authorities say infections and deaths have been under-reported almost everywhere. Thousands have died with COVID-19 symptoms — many in nursing homes, which have been ravaged by a disease that hits the elderly the hardest — without being tested. Four months into the outbreak, nations are still struggling to increase their testing capacity, and many are still far from their goal.

In Italy, officials have acknowledged that the country’s official death toll of more than 22,000 understates the true number, primarily because it doesn’t include those who died in nursing homes and were not tested.

A government survey released Friday of about one-third of Italy’s nursing homes found more than 6,000 residents have died since Feb. 1. It was unclear how many were a result of COVID-19.

In Britain, the official death toll of about 14,600 come under increasing scrutiny because it likewise does not include any deaths at home or in nursing homes. The country’s statistics agency has said the actual number of dead could be around 15 percent higher; others think it will be far more.

And in Spain, the country’s 17 autonomous regions were ordered to adopt uniform criteria on counting the dead.