Portugal reported 646 new coronavirus cases on Wednesday, the highest daily toll since April 20, with transmission primarily occurring in family households, Reuters quoted health secretary of state Jamila Madeira as saying at a news conference.

New cases fell to around 100 a day at the beginning of August but have crept back up since then, worrying the tourism industry as it waits to hear whether it will taken back out of the UK's air bridge list.

Stricter measures to curb the coronavirus outbreak will be introduced across Portugal from mid-September as students return to schools and many workers go back to the office, although details have yet to be announced.

Most new cases were split between the northern region and Greater Lisbon, health ministry data showed.