Greece on Thursday sealed off a migrant camp near Athens after 21 of its residents tested positive for the coronavirus -- beginning with a new mother at an Athens hospital.
"From today the facility is placed under sanitary isolation for two weeks," the migration ministry said in a statement.
Hours before the new cases were announced, Prime Minister Kyriakos Mitsotakis had praised health safeguards at Greek camps.
"I think we're pretty good at contact tracing, and you can actually do contact tracing at the very beginning of an outbreak," Mitsotakis told CNN.
"I think we have a very good track record of dealing with this problem in a very humane manner," the PM said, referring to dire camp overcrowding.
"We will continue to keep a very, very close eye on what is happening in our camps... We're ramping up medical facilities," he said.
The woman from the Ritsona camp, reportedly of African origin, tested positive after giving birth at an Athens hospital this week.
The ministry said that of 63 people subsequently tested at Ritsona, some 80 kilometres (50 miles) north of Athens, 20 were positive but without symptoms.
No staff were found to be carrying the virus, it said.
The new mother's case was the first among asylum-seekers living in a Greek camp. The state has run several vaccination campaigns in past years, but no screening had been done for the present virus.
All access to Ritsona camp has been restricted and food will be delivered to the residents, the migration ministry said. Additional medical staff will be sent to the area and all residents will be screened, it added.
As of 1600 GMT on Wednesday, Greece's population of 11 million had recorded 50 deaths and 1,415 cases of novel coronavirus.