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Boris Johnson has warned of the danger of a “serious spike” in coronavirus infections if people take “liberties” with social distancing rules.

The prime minister sounded the alarm after a “major incident” was declared on Thursday as thousands flocked to the beach to sunbathe in the warm weather. 

Bournemouth, Christchurch and Poole council took the extraordinary step after services were “completely overstretched”. 

Health secretary Matt Hancock, meanwhile, has warned that the government has the power to shut down beauty spots if there is a risk to public health. 

Speaking during a visit to a restaurant in east London, the PM said: “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.

“So in some parts of the world – I won’t name them – you have got spikes, really serious spikes, in the instance of the disease so it is crucial that people understand that on July 4 we get this right, we do this in a balanced way.”

The government has announced that pubs, restaurants, cinemas, theatres and galleries will be among the venues that can open to the public on July 4 as England emerges from the first wave of the disease. 

The two-metre rule on social distancing will also be cut to “one-metre-plus” on the same date, meaning that people can come within a metre of one another provided a “mitigation” such as a face covering is in place. 

But fears remain that the lockdown, imposed in March, is being eased too soon. 

In an interview with TalkRadio, Hancock said he was “reluctant” to go down the route of shutting public spaces as “people have had a pretty tough lockdown”.

But he added that if there was a spike in the number of coronavirus cases “then we will take action”.

Asked about the issue, a Downing Street spokesman told reporters the government could impose local lockdowns, but added: “Everyone should be able to enjoy the sunshine, and we understand that people want to enjoy public spaces, but it is important we don’t undo the hard work of the British public in reducing the transmission of this virus.

“It is a matter for local authorities to manage numbers, alongside emergency services and Public Health England.

“As we saw yesterday they are best placed to make those decisions on a case-by-case basis.” 

Pressed on whether the government would close beaches, the Number 10 spokesman said: “It is for local authorities to manage numbers.

“I believe Matt Hancock, when he spoke, was referring to the powers to impose localised lockdowns which we have been clear throughout may need to be the case if we see case numbers rise in a particular area.”

Chief medical officer for England Professor Chris Whitty has also urged people to follow social distancing rules in the hot weather or risk causing a spike in coronavirus.

He wrote on Twitter: “Covid-19 has gone down due to the efforts of everyone but is still in general circulation.

“If we do not follow social distancing guidance then cases will rise again.

“Naturally people will want to enjoy the sun but we need to do so in a way that is safe for all.”