Whitty 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."
A major incident was declared at Bournemouth Beach after thousands of people crowded onto the sand with little if any space between them.
Another incident was declared at Formby Beach in Merseyside, where police were called-in to break up large crowds.