Seven thousand policemen will be deployed to protect Germany's chancellor, Angela Merkel, during her visit to Athens.
Merkel is due to hold talks with Greek prime minister Antonis Samaras in her first visit to Athens in five years.
Large areas of the capital are expected to be closed in a security crackdown as anti-austerity and anti-Merkel rallies take place.
"She does not come to support Greece, which her policies have brought to the brink. She comes to save the corrupt, disgraced and servile political system. We will give her the welcome she deserves," said Alexis Tsipras, leader of the Greek opposition part,y Syriza.
Merged in a deep economic crisis, Greece is surviving because of bailouts from other countries. Germany has a prominent role in the scheme.
In return, the Greek government has had to promise severe budget cutbacks and tax hikes which have hurt ordinary Greeks hard and led to widespread anger.
Merkel is seen by many Greeks as a tyrant who aims to reduce their country to economic slavery.
The economic crisis has rekindled anti-German sentiment that goes back to the Nazi occupation of Greece during the Second World War.
Over the next two years Athens is expected to implement further cuts of €13.5 billion (£11bn).
Merkel will be in Athens to express her support for the ambitious reforms of the Greek government, her spokesman, Steffen Seibert, said.