Greek Prime Minister Kyriakos Mitsotakis on Thursday declared a night curfew in Athens, Thessaloniki and other areas to curb the spread of the novel coronavirus.

"We aim to reduce circulation and night gatherings that favour the spread of the virus," Mitsotakis said in a televised address, in which he also announced the "compulsory" use of masks both indoors and outdoors in the worst-hit areas.

"The mask is the vaccine before the vaccine (arrives)," the PM said.

The curfew from 0030 to 0500 that comes into force on Saturday was announced after a record 882 new infections and 15 deaths were earlier announced by the state health agency.

"We've seen a sudden increase in cases in recent days," Mitsotakis said, a trend he partially attributed to additional testing.

The PM said the measures were applicable to areas with "dangerous" case increases.

Mitsotakis said that Greece "continues to resist better than most other European countries", adding that he preferred local-level measures ro a general lockdown.

The latest death toll is the highest since the pandemic arrived in Greece in February.

Greece has now registered over 28,000 cases and nearly 550 deaths, with infections steadily rising since August.

Another 90 people are in intensive care.

Health authorities in recent days have warned that the average age of new infections has fallen to below 40.

State efforts to discourage gatherings by shutting down restaurants, clubs and kiosks at night have only proved partially successful, as young Greeks continue to meet in large groups in squares, university grounds and other public areas.

"Now is not the time for clandestine parties... we are more vulnerable at carefree moments," Mitsotakis said.

On Wednesday, a retirement homeowner killed himself with a shotgun after three confirmed cases in his institution in northern Athens.

The death of Dimitris Kampanaros, a widely respected gerontology expert, made headlines in the country.