For an extension of your entrance visa, you will need to speak with the consulate or embassy of China in Greece to advise you on how to proceed.
How can I apply to extend my stay in Greece as a potential Golden Visa applicant?
I am a potential Golden Visa applicant from China. I entered Greece to conduct due diligence on properties for my application shortly before the coronavirus outbreak happened. I was worried about the virus so I kept staying in Greece. My visa is about to expire. How can I apply to extend my visa and keep staying in Greece legally?
If you wish to stay beyond 90 days, you must visit an aliens bureau and show evidence of a compelling reason to prolong your stay in Greece at least two weeks before the end of the 90 day period. Please note that extensions for tourist purposes are not granted.
You should apply for an extension of your Schengen Visa (valid only for the Greek territory) before the expiration of 90 days period. You might be able to obtain an extension valid for another 90 days. It is only valid for staying within the Greek territory. If you travel out of Greece, the remaining days are lost. In order to apply for an extension, you need a confirmation of hospitality by a Greek resident; an insurance contract; a valid passport and two photos; payment of governmental fees; a bank check issued on your name with an amount equal to 4,500 euros (90 days by 50 euros per day). You also need an attorney to handle your case.