The Royal Cornwall Hospital Trust said there has been a "spike in admissions" ahead of the half term holiday which begins today for many schoolchildren.
Dr Toby Slade, an emergency department consultant, said: "The rise in admissions isn’t related to coronavirus or holidaymakers but we are seeing more poorly people, particularly elderly patients, who need our care.
"With more people likely to be heading to the county over the next few days we want to remind residents and those coming to stay, to first call their own GP, even if they are here on holiday, when they need care for something that’s urgent by not serious or life-threatening."
Mr Slade said people should go online to www.111.nhs.uk if outside of GP surgery hours, or call 111 for advice.
He said: "We’re doing really well in Cornwall to keep levels of the virus low and need the continued support of patients by using the right services and not coming to our emergency department unless they really need to.”