Those aged over 60 are now being told to "minimise their contact with others" and follow the same advice given to "clinically vulnerable" people, in order to avoid catching coronavirus.
The comments from Boris Johnson followed those of his spokesperson, who told reporters: “The over 60s should take extra care because there is evidence they could be at greater risk of becoming seriously ill.
“The scientific advice is that people in the over 60 age group do have a higher risk of becoming more unwell with coronavirus, so they should take extra precaution.”
Advice for the clinically vulnerable previously only applied to those over 70, or with underlying health condition, but new guidance - which comes into force when England's lockdown is implemented on Thursday - has been extended to over 60s.
Mr Johnson, updating MPs in the House of Commons of his plans for an England-wide lockdown, said: “The clinically vulnerable and those over 60 should minimise their contact with others. “And while we will not ask people to shield again in the same way, the clinically extremely vulnerable should only work from home.”
In the press conference he held to announce the new lockdown in England, Mr Johnson said: "If you are clinically vulnerable, or over the age of 60, you should be especially careful to follow the rules and minimise your contacts with others.”
While the official government guidance does not explicitly identify over-60s as "clinically vulnerable, it says they should follow the same advice.
The government website says: "If you are over 60 or clinically vulnerable, you could be at higher risk of severe illness from coronavirus."
Anyone in this group should "be especially careful to follow the rules and minimise your contacts with others".
They should also "continue to wash your hands carefully and more frequently than usual and maintain thorough cleaning of frequently touched areas in your home and/or workspace".
There is separate advice for the clinically extremely vulnerable (CEV) - the 2.2 million people who were contacted by the NHS and asked to shield in March.
CEVs are "encouraged to stay at home as much as possible, but are encouraged to go outside for exercise".
The government's full guidance for CEVs can be found here.