When Vladimir Putin sat down for a briefing on coronavirus, Moscow’s mayor had a tough message for him: the number of infected people is far higher than you’ve been told, he said, and Russia’s healthcare system could be overrun.

Breaking with official tallies that show the disease’s conservative growth in Russia, Sergei Sobyanin told Putin on Tuesday that a serious situation was developing as the disease spread in Moscow and in the regions, and that the problem “would emerge sooner or later”.

Sobyanin estimated that the number of people who are ill in the capital may have reached 500, far higher than the 290 that have been identified by Russian doctors.

The remarks, apparently backed by municipal data, will confirm doubts about the Kremlin’s claims that it has the coronavirus outbreak under control.

“The growth is high; a serious situation is developing,” Sobyanin told Putin and top aides during the meeting. Many sick people were isolated at home and had not asked for medical care, he said. “The number who are really sick is far higher [than official estimates].” The remarks were reported on the Kremlin website.

Russia has been an international outlier in terms of coronavirus testing, claiming to have identified just 500 cases of the disease despite having carried out more than 165,000 tests. By comparison, just 70,000 people have been tested for coronavirus in the UK, with 6,650 confirmed cases of the disease. Neighbouring Belarus has an infection rate that is three times higher per capita.

Critics have questioned whether Russia’s tests were effective at identifying those ill with the virus, and whether cases of coronavirus had not been mischaracterised as pneumonia in an effort to massage the official numbers and prevent panic. Earlier, the business newspaper RBC had reported that numbers of pneumonia patients in Russian hospitals had jumped more than 30% between January 2019 and January 2020, indicating that coronavirus patients may have been misdiagnosed.

Sobyanin’s remarks made him the first senior Russian official to publicly contradict the official tally and directly urge greater action from the Russian president in response to the outbreak. He called for prophylactic measures to be taken by the heads of all of Russia’s regions, including the extension of a self-isolation regime for elderly Russians considered most at-risk from the disease.

He also saidthat Russia’s healthcare system could be overwhelmed if it was not prepared for a rise in patients, and urged greater testing throughout the country.

“No one in the world knows the real picture,” Sobyanin said.

The Kremlin has largely presented the situation with the disease as under control, with top officials including Putin telling the public that the greatest danger was panic. But Tuesday marked a change in the government’s rhetoric, with Putin suddenly donning a yellow protective suit and respirator to tour the capital’s main hospital for coronavirus patients.

Earlier on Tuesday, a woman died at the hospital in Kommunarka. Doctors claimed she had not been ill with coronavirus, and had died because of complications from cancer. Russia has tallied only one death linked to the virus.