Russian doctors are preparing for an “explosive” escalation of the coronavirus situation across the country as the country’s number of cases began to increase exponentially, Moscow’s top infectious diseases specialist said Wednesday.

As of Thursday, Russia has confirmed 840 cases of coronavirus and three deaths. Wednesday and Thursday saw Russia’s largest one-day increases in new cases as Moscow Mayor Sergei Sobyanin warned President Vladimir Putin that the real number of cases is likely much higher than official numbers suggest.

Nikolai Malyshev, the chief infectious diseases specialist in the Moscow Health Ministry, warned that an “explosive development like a nuclear reaction” is not out of the question, suggesting that “a huge number of people will be infected.”

“At first, we saw an linear increase of patients. But now it is exponential. Over the past day, the infection rate has almost tripled,” the RBC news website quoted Malyshev as saying in a television interview.

Malyshev said that new hospitals and beds are being readied across Russia to prepare for the potential influx of new cases.

Starting March 27, Russia will suspend all regular and charter flights to other countries in an effort to slow the spread of the infection within its borders, while Moscow will close all restaurants, cafes, non-essential shops and parks for a week starting Saturday.

President Vladimir Putin declared that next week will be a national holiday to encourage people to stay at home – a move that observers have criticized as an ineffective measure to stop the pandemic’s spread.