Restrictions on domestic flights are extended to May 10, the Civil Aviation Authority (CYA) said.
Only necessary travel is allowed between Greek airports, it added.
In addition, CYA is expanding the list of countries whose nationals may enter Greece without a seven-day isolation. Passengers must however have been vaccinated or present a negative Covid-19 test.
Nationals who no longer have to self-isolate after arriving in Greece include those of Australia, New Zealand, South Korea, Russian, Rwanda, Singapore and Thailand.
Permanent residents of the European Union, Schengen Treaty countries, the United Kingdom, the United States, the United Arab Emirates, Serbia and Israel may enter Greece if they are vaccinated or present negative results for a PCR test.
Russian citizens will be able to enter Greece through nine airports (instead of the former three), as long as they also present the above-mentioned documents. PCR tests are also required of children above 5 years of age arriving with their families.