Deputy Minister for Civil Protection & Crisis Management Nikos Hardalias strongly recommended during a live briefing on Thursday that travellers on the mainland make use of COVID-19 self-tests, but added there was no restriction in travel in the area.
He recapped all standing restrictions for adults travelling to and from Greek islands by ferry or airplane (into effect as of July 5).
The Deputy Minister stressed that although children under 12 don't face travel restrictions, they should be given a self-test upon returning from islands.
Hardalias also provided the latest pandemic alert status in Greece's prefectures, including a notching up to orange for the southern neighbourhoods of Athens.
Commenting on the rapid increase in new infections, doctor Vana Papaevangelou said that the increase concerns mostly young people.
The median age of those infected is 23 years, she said, a drop of a whole decade within a week.
Of all new infections, 75% are younger than 34 years, and the largest single age group is 15-24.
One in three hospitalisations for COVID-19 relate to people aged 25-55, she revealed, while 1 in 10 is under 24.
Papaevangelou said that 121 cases of the Delta variant have been officially registered in Greece so far, mostly concerning people under 40.
Of the total, 13% had to be hospitalised, with none being fully vaccinated, she added.
Doctor Gkikas Magiorkinis noted at the briefing that deaths from COVID-19 had dropped by 50% in Greece.