Local authorities ordered guests not to leave the resort on Monday after the case was detected at the Santo Stefano resort, on Sardinia's La Maddalena island.
The region's crisis unit conducted swab tests on some 470 vacationers and staff on Monday.
“We are waiting for the swabs to be processed, in the meantime we have arranged that no one leaves the resort,” stated regional health councilor Mario Nieddu.
Guests are allowed to move freely around the resort itself, but mustn't leave, Italian media reports.
Two guests reportedly tried to escape shortly after the lockdown was ordered, but were stopped by local police on their way to Olbia airport.
Over the weekend, Italian authorities ordered the closure of nightclubs and tightened mask-wearing rules after the number of new cases detected in the country rose from 200-300 to 600 within one week.
Many of Italy's new cases have been attributed to holidaymakers – often Italians returning from abroad, health authorities said.
Italy reported 403 new positive cases within 24 hours on Tuesday, and five deaths.
The total number of Italian cases recorded since the start of the pandemic is now over 254,000, while the death toll has passed 35,400.
Italy is the second-hardest hit country in Europe after the UK in terms of deaths from Covid-19, and was the first country outside of China to suffer an outbreak of Covid-19. However, Italy is generally viewed as having managed the crisis relatively well, with infection rates dropping following a strict and lengthy lockdown.
Italian government ministers and health experts have repeatedly insisted that though cases have been rising again, they can be kept under control.
Authorities are urging people to continue to take basic precautions – wearing masks in public places, frequent hand-washing, and maintaining a distance from others.