Spikes in coronavirus cases abroad should act as a warning to Britons who flout social distancing rules, Boris Johnson has said.
The PM said crowds on Bournemouth beach on Thursday suggested people needed to understand that “mingling too much” could set the UK back.
He said people in other countries had been “taking too many liberties with the guidance” as lockdown rules eased.
Ministers have warned UK beaches could be closed if infections rise.
A further 186 deaths of people who had tested positive for coronavirus in the UK were announced on Friday, with the total number to have died now standing at 43,414.
The latest figures, released by the Department for Health and Social Care, showed a further 1,006 people had tested positive for the virus.
Mr Johnson said people in some countries were “not observing social distancing”.
“Some parts of the world – I won’t name them – but have you have got spikes, really serious spikes in instances of the disease, so it’s crucial that people understand that on 4 July we get this right, that we do this in a balanced way, and we recognise the risks,” he said.
“You may think you are not going to get it, that you’re immortal and invincible and so on – and very likely that’s true if you are young person. But the bug you carry can kill elderly people particularly. It is still dangerous; the virus is still out there.”
The prime minister was speaking after the World Health Organization said Europe had seen an increase in weekly cases of Covid-19 for the first time in months after restrictions were eased.