The prime minister urged Britons to refrain from "mingling too much and not observing social distancing".
A major incident was declared in one south coast town after hordes of sun-seekers flocked to the seaside on Thursday.
Speaking on Friday, Mr Johnson said: "Let me be very clear about the scenes in Bournemouth - it's very important for people to understand if you look at what's happening elsewhere in the world where people have been coming out of lockdown.
"I'm afraid what you're also seeing is people taking too many liberties with the guidance, mingling too much, not observing social distancing.
"In some parts of the world - I won't name them - you've got really serious spikes in the instances of the diseases."
The prime minister urged people to follow the rules until they change in England next Saturday.
"It's crucial people understand that on 4 July we get this right and we do this in a balanced way and we recognise the risks," he said.
"You may think you're not going to get it and you're immortal and invincible and so on. And very likely that's true, particularly if you're a young person.
"But the bug you carry can kill elderly people particularly. It's still dangerous. The virus is still out there."
Downing Street signaled there are no plans to close beaches, as the health secretary suggested, and that it is up to councils to step in and manage over-crowded destinations.
The prime minister's spokesman did add that local lockdowns could come into force if rates of the virus shoot up, but not preemptively.
George Eustice, the environment secretary, conceded to Sky News that "clearly people didn't heed" two-metres social distancing after the beach overcrowding scenes and illegal raves in London.
"It's inevitably the case that as you start to ease these restrictions and you drop some, the ones that are left sometimes look inconsistent with that," he said.
Several Labour MPs have criticised Mr Johnson sticking by his top aide Dominic Cummings, who police said may have broken lockdown rules for allegedly making a 30-minute drive to test his eyesight while Britons were being told to "stay at home".
Neil Coyle tweeted: "When he failed to sack Cummings he lost any grounds to criticise anyone else 'taking liberties'."
And Barry Sheerman claimed: "Someone please tell Boris Johnson no one takes any notice of his advice since his fiasco with rule-breaker Cummings!"