The UK is moving into the next stage of its response to the coronavirus outbreak, England's chief medical officer has told MPs.
Professor Chris Whitty said the UK was "mainly" in the "delay" phase of the government's four-stage approach to COVID-19.
Efforts had initially been made to try and contain the spread of the disease, but Prof Whitty - who is helping to coordinate the UK's response - said it was now "optimistic" to believe this could be a success.
"We have moved from a situation where we are mainly in contain, with some delay built in, to we are now mainly delay," he told the House of Commons health committee.
The UK is now hoping to push back the peak of a coronavirus outbreak until the summer months, when there will be less winter pressures on the NHS and will allow more time to research the disease.
However, the prime minister's spokesman later sought to clarify that the UK was still in the contain phase and, if a decision is made to move to the delay stage, then it would be announced publicly.
After hearing from Prof Whitty, former Conservative leadership contender and now health committee chair Jeremy Hunt told Sky News: "The virus has now moved from contain to delay stage.
"There are very active preparations for the final stage, the mitigate stage."
Prof Whitty also outlined how there could possibly be a seasonal element to COVID-19, which means the rate of transmission slows down in warmer weather.
As the government moves through the various stages of its coronavirus response, it will take increasing action.
This could include closing schools, reducing large scale gatherings and encouraging working from home.
Non-urgent NHS operations could be postponed, retired doctors might be called back to work, and police could be told to concentrate on only serious crime, the government has also said.
The four stages of UK's coronavirus response:
As time goes by, there would be measures that involved "changes to society", Prof Whitty said.
Prime Minister Boris Johnson stressed the "overwhelming majority of people" who are infected with coronavirus would suffer only a "mild to moderate illness".
"We are still at the stage where the single best thing we can do... is just wash our hands," he told ITV's This Morning.
Mr Johnson said the government's Scientific Advisory Group for Emergencies (Sage) was on Thursday considering a range of options to delay the spread of the disease.
"At the moment what they are telling me is, actually, slightly counter-intuitively, things like closing schools and stopping big gatherings don't work as well perhaps as people think in stopping the spread," he said.
The prime minister denied the government was witholding information about the virus following criticism of a move away from providing daily updates on the locations of new UK cases.
He said: "Let me clear that up immediately because it is very important that we are transparent, people understand that we are transparent.
"Public Health England needs to be absolutely sure about the diagnosis of these cases so what they are doing is they are immediately identifying the region where they think there's an incidence and then within 24 hours confirming the exact location to be sure that we have got the right thing."
The prime minister suggested there would be help for businesses impacted by coronavirus in next week's budget.
Prof Whitty admitted there had been a "communications fumble" over the reporting of information of the location of each new COVID-19 case.
"We are intending to provide geographical information - in fact, in the medium term we will provide a lot more information with maps and other things, with a proper dashboard as we gradually move into a phase where there are many more cases," he said.
"What we are, though, intending to do is have some delay - about 24 hours - to be absolutely sure we've got the details right."
In other developments:
The current number of COVID-19 cases in the UK stands at 90, but Prof Whitty is "expecting the number only to go up" later on Thursday and over the coming weeks.
"There are now several, not large numbers but several cases where we can't see where this has come from in terms of a clear transmission - either because someone's come directly from overseas, or they've had close contact with someone who's recently returned from overseas," he added.
"That makes it highly likely, therefore, there is some level of community transmission of this virus in the UK now."
Prof Whitty said he had a "reasonably high degree of confidence" that 1% is at the "upper limit" of the death rate for coronavirus.
But, although the number of deaths could be a "very small number" as a proportion, it might be a "large absolute number" depending on how many are infected, he added.
MPs were told there are plans in place if mortuaries struggle for space amid an increase in deaths, but Prof Whitty stressed that, even for high-risk age groups, contracting COVID-19 did not mean you would be "a goner".
There is about a five-day period between being infected by the virus and the onset of symptoms, he said.
Prof Whitty said there was "no need" for Britons to stockpile food or medicine, saying the impact of the virus would be "a marathon not a sprint", but he suggested now "is a very good moment" for smokers to quit.
Virus Outbreak: Global Emergency - Watch a special Sky News programme on coronavirus at 6pm weekdays