Greece's high schools reopened on Monday after a five-month closure to curb coronavirus infections with precautions including virus tests for students and teachers twice per week, the education minister said.

High school classes had been held online since November 7. Monday's reopening saw some schools hold classes outdoors.

Primary and secondary schools, which had briefly reopened, remain closed across the country.

Every Monday and Thursday, high school students and teachers will have to be screened for Covid-19 with self-tests available free in pharmacies. 

"These self-tests will be a valuable tool," Education Minister Niki Kerameus told ERT television.

A positive self-test will result in a 48-hour quarantine and another screening in a clinic. A second positive test will lead to 14 days of quarantine.

For the first day back, 613 students and teachers tested positive on self-tests, the majority showing no symptoms, according to the prime minister's office.

Students and teachers must also wear masks, recess will be staggered to limit crowds and canteens will be closed.

Prime Minister Kyriakos Mitsotakis said Monday that self-tests will be extended from the end of this week to employees at stores as well as those working in transport and food delivery. "It's a weapon to limit the virus's transmission," he said.

With the country still in the grip of the pandemic, the reopening has worried some health experts.

Greece has reported more than 293,000 infections and over 8,800 deaths since the start of the pandemic. 

On Sunday, 1,718 new cases were reported, and hospitals in Athens and Thessaloniki remain overcrowded.