LONDON -- British Prime Minister Boris Johnson described the reopening of schools in England as a "national effort" to beat coronavirus, even though some experts warned Britain is still not "out of the woods", local media reported Sunday.

"The reopening of schools marks a truly national effort to beat this virus," Johnson told Sky News.

"It is because of the determination of every person in this country that we can start moving closer to a sense of normality -- and it is right that getting our young people back into the classroom is the first step," he was quoted by Sky News as saying.

On Feb 22, Johnson announced his long-anticipated "roadmap" exiting the lockdown. Schools in England will reopen from Monday as first part of the four-step plan, which Johnson said was designed to be "cautious but irreversible".

Under the guidance, secondary schools students across England are to receive three COVID-19 lateral-flow tests before using at-home kits twice a week.

British Education Secretary Gavin Williamson said that Monday will "mark a moment of joy for millions of people across the country".

"I do not underestimate how challenging the last few months have been with some children in class and most at home, but I do know how important it is for all children to be back in school, not only for their education but for their mental health and wellbeing," he said.

More than 21.7 million people in Britain have been given the first jab of the coronavirus vaccine, according to the latest official figures.

British Health Secretary Matt Hancock has confirmed that two-fifths of Britain's entire adult population have now been vaccinated and the government is "on course" to offering a first vaccine dose to all adults by the end of July.

However, experts have warned Britain is "still not out of the woods" amid concerns over new variants and the risks of the public breaching restriction rules.

"We have done fantastically well in the last couple of months but we are not completely out of the woods yet," Britain's National Statistician Ian Diamond said Saturday.

"I'm in very much the view that we should do everything we can not to blow it nationally," Diamond added.

England is currently under the third national lockdown since outbreak of the pandemic in the country. Similar restriction measures are also in place in Scotland, Wales and Northern Ireland.

To bring life back to normal, countries such as Britain, China, Germany, Russia and the United States have been racing against time to roll out coronavirus vaccines.