"It has been very difficult in recent times - we are very happy this happened," the Secretary of State for health, Antonio Sales, said as he teared up during a news conference.
"I want to leave this message of hope to the Portuguese but I want to ask them to help us maintain these numbers," he said.
Portugal's total confirmed cases rose by 106 from Sunday to 51,569, with 62% of new infections reported in and around Lisbon, where localized outbreaks on the outskirts have worried authorities for the past two months.
The death toll remained unchanged at 1,738.
The country, heavily dependent on tourism, began lifting restrictions imposed during a six-week lockdown on May 4 and was initially hailed as a success story in its fight against the disease.
But the outbreaks around Lisbon forced the government to reinstate some measures in affected areas, and led several European nations, including Ireland, Belgium and Finland, to impose travel restrictions on Portugal.
Portugal was also left off a list of dozens of countries Britain considered safe enough for travel without having to quarantine upon return.The need for holidaymakers returning to Britain from Portugal to quarantine for 14 days has particularly affected the Algarve, a region popular for its beaches and golf courses.