Russia has recorded 10,633 new COVID-19 cases - the highest daily tally since the beginning of lockdown and almost double the number announced last week.
More than half of Sunday's new infections were in Moscow.
Sergei Sobyanin, mayor of the Russian capital, thinks health authorities are underestimating the overall number of those hit by the disease.
He says up to 2 per cent of Moscow's population could be infected — about 240,000 people. That is more than the official total number of cases across the whole of Russia: 145,268.
Official data in question
The official death toll is also being questioned. According to the authorities, at least 1,356 people have died from COVID-19 in the country.
But many think the real figure is a lot higher.
Anastasia Vasilyeva, the head of Russia's Alliance of Doctors union, said authorities are classifying many coronavirus cases as ordinary pneumonia, of which there is an outbreak in the country.
Health experts say the scale of the outbreak in Russia remains unknown because of the unreliable nature of official statistics.
And the country's health system is already struggling to cope. Moscow's hospitals are working at capacity and temporary facilities are being quickly set up in sports complexes and shopping malls.
Medical workers are urging the government and local organisations to provide more protective equipment. And anger is growing among healthcare workers as more than 20 hospitals had to quarantine after many of their staff were infected.
Outside the big cities, the situation is a lot worse. Medical equipment is severely lacking, some hospitals have less than five respirators.
Students to the rescue
To alleviate the pressure felt by medical staff, the government has called on students to work in hospitals as part of their training.
Authorities have drawn up a map of the outbreak, placing some regions in red zones where many are infected and others in white zones where there are fewer cases.
Medical students don't have to work in the red zones but some say this isn't reassuring because even in the safer zones they are being sent to the frontlines without appropriate protection.
Aleksandra is one of the leaders of a movement striving to get more guarantees from health authorities. She is very worried about the risk of infection.
"We are taken and sent with this unspecified order to plug gaps in these hospitals," she said. "This is dangerous work, we risk infection, it can’t just be considered as educational practice."
Students can't refuse to work in the hospitals without it affecting their grades and in the long run, they could face expulsion.
Aleksandra says students aren't opposed to the idea of being able to practice what they have learnt and help others but they can't put their own lives at risk.
Last week President Vladimir Putin announced the country's lockdown would be extended to May 11. He said the outbreak hadn't yet reached its peak in Russia.