Boris Johnson said people in England “should wear” face masks or other coverings inside stores to help prevent the spread of the coronavirus.
The Prime Minister said that the government would decide in the coming days whether “enforcement tools” were needed.
The comments follow cabinet minister Michael Gove, who told the BBC on Sunday that face covers should not be made compulsory in stores in England.
The Labor party demanded “urgent clarity” from the government on the issue.
Face covers are worn to prevent carriers from spreading the coronavirus, rather than catching it.
Currently, they are mandatory on public transport in England, Scotland and Northern Ireland – and the Welsh government has announced that it will apply the same measure from July 27.
In Scotland, coatings are also compulsory in stores, but critics have complained that the situation in England must be easier for the public to understand.
The World Health Organization (WHO) says that homemade cloth masks or face cloths should be worn in public where social distancing is not possible to reduce the spread of coronavirus droplets.
He changed his mind last month, after arguing that there was not enough scientific evidence to say that healthy people should use them.
Visiting paramedics in central London, Mr Johnson, whose government controls health policy in England but not the rest of the United Kingdom, said: “I think people should wear [face masks] in the shops.
“And, in terms of how we do it, whether we make it mandatory or not, we’ll be looking at the guidelines – we’ll see a little bit more in the coming days. ”
Johnson added, “Throughout this crisis, people have shown incredible sensitivity to others and an understanding of the needs to fight the virus by acting in cooperation.
“Wearing masks is one of them… It is a reciprocal thing; people see the value. We will see in the coming days exactly how – with what application tools – we think we want to progress. ”
Analysis by Helen Catt, political correspondent
Signs seem to indicate that the government is making masks mandatory in more places in England, but the ministers seem reluctant to get involved yet.
Michael Gove’s preference for trying to encourage people to take voluntary action – rather than for fear of enforcement – is what we have seen the government repeat throughout the pandemic.
But the accompanying risk is that of mixed messaging. Earlier, when the coronavirus was more widespread, he said that the scientific evidence for wearing the mask was not clear enough. Now, he says, the evidence is stronger.
Of course, the scientific understanding of the virus is constantly evolving, and so is likely to be the case as well.
If the government now believes that masks are the way to go, it will be essential to communicate this message without confusion.
The Prime Minister said on Friday, “I think we need to be tougher on insisting that people wear face covers in confined spaces where they meet people they don’t normally meet.”
But on Sunday, Cabinet Minister Gove told the BBC’s Andrew Marr Show that he did not think wearing masks in stores in England should be mandatory, adding that he would “encourage” them to do it “where they are likely to mix with others. and where ventilation may not be as good as it could be. “
He added: “I think it is good manners, courtesy and consideration, to wear a mask if you are, for example, in a store. ”
Shadow Secretary for Occupational Health Jonathan Ashworth said that “conflicting advice and conflicting government statements only hinder our fight against the virus.”
He wrote to the Secretary of Health, Matt Hancock, asking him to “define the position on the face covers urgently”.
“With the lockdown rules being relaxed further this week, it is essential that updated guidance on this issue be released by the government without delay,” said Ashworth.