Greece on Thursday recorded more than 5,000 coronavirus cases after a spurt in new infections that sparked a "wake-up week".
The national public health organisation announced 153 cases over the last 24 hours, raising the total to over 5,100. There have been 210 deaths so far.
The highest amount of daily cases announced was 156 on April 21, following a mass outbreak at a migrant hotel near Athens.
Late on Thursday, the civil protection agency announced emergency restrictions on the small holiday island of Poros near Athens.
These include a night curfew for all restaurants and bars to August 17 and a ban on fairs and open markets after over a dozen cases were reported on the island.
A ban on gatherings of over nine people was declared on Poros, even inside homes, and masks have been made obligatory both outdoors and indoors.
Greece on Wednesday announced a "wake-up week" on COVID-19, tightening restrictions after the steady rise in mostly domestic infections.
Officials have blamed the increase on overcrowding in clubs and social events.
Only 10 percent of cases in Greece can be traced to foreign arrivals, Prime Minister Kyriakos Mitsotakis told a cabinet meeting on Wednesday.
Earlier Thursday, the government said Greece's land borders would close at night to travellers, except one crossing with Bulgaria.
"We have located three sources of concern: very regular crossings from Balkan countries by ethnic Greeks and residence permit holders... social gatherings, including clubbing youths, weddings and baptisms, and public transport," Petsas said.
The public protection agency last week said masks must be worn in all indoor public areas, and visits to retirement homes and other institutions hosting vulnerable groups are restricted until August 15.
A limit of 100 guests was also set for weddings, baptisms and funerals, and summer fairs were cancelled.
Mitsotakis has already ruled out a general lockdown after gradually reopening the economy in May and starting to accept foreign arrivals in June to salvage part of the tourism season that is vital to the economy.