England on Tuesday entered a strict national lockdown aimed at stemming a steep rise in virus cases that a senior government minister warned could last into March.

Prime Minister Boris Johnson announced the measures, including school closures and a ban on leaving home except for exercise and essential shopping, on Monday evening.

Cabinet Office minister Michael Gove told Sky News on Tuesday morning that he could not say precisely when the lockdown, announced as lasting six weeks, would be lifted, warning of "very, very difficult weeks".

The measures will be reviewed from February 15, he said, but the government cannot "predict with certainty" whether they will be lifted then.

-I think it is right to say that as we enter March we should be able to lift some of these restrictions but not necessarily all- he added.

The measures began in England on Tuesday morning and will become law in the early hours of Wednesday morning.

Scotland, Wales and Northern Ireland are also bringing in strict lockdowns including school closures.

The lockdown comes as the surge of a new strain of the virus that is said to be more infectious threatens to overwhelm hospitals, despite the rollout of two vaccines, including UK's own Oxford University/AstraZeneca shot from Monday, bringing hopes of beating the virus in the coming months.

The UK has already vaccinated over one million people.

A total of 58,784 people tested positive in the UK on Monday, with cases in the last seven days up 50 percent on the previous week.

Schoolchildren will not sit crucial end-of-year exams needed to enter higher education as usual, Gove said.

-We will be putting in place alternative arrangements- he said.

He also said the UK could impose new restrictions on international travel. Currently quarantine is compulsory for those arriving from some countries but not virus testing.

Gove said he had discussed this with the leaders of the other UK nations, adding: "We will be coming forward very shortly with new proposals."

Overall, Britain has been among the worst hit in the world by the outbreak, with some 2.7 million cases and 75,431 deaths.

Johnson was widely criticised for hesitating too long about the measures, particularly school closures.

But he won some support on Tuesday. The Times wrote: "Mr Johnson said that the weeks ahead would be the hardest yet. But at least we have given ourselves a fighting chance."