Speaking outside Downing Street in London, Johnson said that the UK was making progress in tackling the outbreak, with fewer ICU hospital admissions for Covid-19 patients, and "real signs now that we are passing through the peak."
The virus has killed more than 20,000 people in the UK.
"If this virus were a physical assailant, an unexpected and invisible mugger, which I can tell you from personal experience it is, then this is the moment when we are beginning to wrestle it to the floor," Johnson said.
But he warned that the UK was at a moment of "maximum risk" as people's patience might be fraying with the restrictive measures imposed to stop the spread of the virus.
Johnson said he understood the worries of shopkeepers and entrepreneurs, and that without a functioning economy there was no way of funding the NHS.
But he warned that he "refused to throw away all the effort and sacrifice of British people" and risk a second peak of the disease and further loss of life by relaxing those restrictions too soon.
Johnson also thanked Foreign Secretary Dominic Raab for deputizing for him, saying: ''I'm sorry I've been away from my desk for much longer than I would have liked."