Anti-riot police in Athens on Thursday fired tear gas toward hooded youths who lobbed firebombs and flares at them during a protest by pupils over the risks of coronavirus in schools.

The skirmishes between the police and the small group flared outside parliament as some 3,000 people, mainly high school pupils, demonstrated, AFP reporters on the scene said.

Hundreds of schools around the country are shut by sit-ins, with pupils protesting against the education ministry's decision to allow classes of up to 30 participants at a time of increasing coronavirus infections.

Nearly 400 people have died in Greece from the virus since February, with the infection rate accelerating from August onwards.

Opposition parties have criticised the government, arguing that packed classrooms are contrary to social distancing rules.

The education ministry counters that fewer than five percent of classes nationwide are overcrowded.

Pupil groups also reject ministry plans to apply distance learning in schools shut by sit-ins, arguing that many schools lack the necessary infrastructure.