Police in Athens were on high alert on Monday for this week's visit by German Chancellor Angela Merkel, bracing for street protests against the leader of Europe's paymaster who has become a hate figure to many over punishing austerity cuts.
About 6,500 police, backed by water cannon and a helicopter, will be on the streets for Tuesday's trip alongside about 300 members of the coastguard, and Athens city centre will be sealed off, a police source said.
Greece's police minister has appealed for calm as the leftist leader of the opposition said the gatherings called by parties including his own and unions for Tuesday would be "peaceful and populous".
Merkel is a popular hate figure in Greece, often blamed for harsh austerity measures imposed by the government in return for vital international aid, and has in the past been depicted as Adolf Hitler in tabloid caricatures.
Last month, during a general strike against spending cuts, protesters marching past the Bank of Greece crossed out "Greece" on the bank's sign and wrote "Merkel" over it.
Alexis Tsipras, the head of the main opposition Syriza party that has a leading role in Tuesday's planned protests said: "The Greek people will deliver an answer in a peaceful and populous manner...we believe it will be a message of democracy.
"What is happening in our country is unprecedented and criminal," he said, pointing to a three-year austerity programme "leading to social collapse".
"It might be a useful visit for Merkel to realise that this policy cannot proceed and lead to a change of strategy," the leftist leader added.
Police have declared a ban effective on Tuesday on "public gatherings and demonstrations" in a broad section of the city centre that includes the German embassy, parliament and the offices of government but union gatherings lie outside this area and will be held as planned.
"I appeal to all Greeks and to those who want to protest, to safeguard peace in the capital," Public Order Minister Nikos Dendias said.
"Above all, our country's prospects and its image abroad," he said.
Merkel will meet conservative Prime Minister Antonis Samaras in Athens on her first visit to the debt-crippled country since the beginning of the Greek financial crisis almost three years ago.
Government spokesman Simos Kedikoglou told Antenna television that the visit is "message of faith in the course of the Greek government, the Greek economy.
"It is a positive step, it's important that the German chancellor is coming to Greece for the first time since the start of the crisis," he said.
Merkel's office said she was bringing a message of support for "ambitious" cuts already in place in Athens and encouragement to maintain the efforts.
During the visit, special security precautions will also be taken for the German embassy and other German-affiliated buildings, the Athens News Agency reported.
Samaras has assured Merkel that she will be "welcomed in the appropriate way for the leader of a major power and a friendly country", but many in Greece object to the visit.
Some 3,000 people gathered on Monday evening around central Syntagma Square in an anti-austerity protest scheduled before Merkel's visit was announced.
"Rise up so that the people doesn't go bankrupt," a group of hotel workers affiliated to the Communist party shouted near the finance ministry.
Outside parliament, another group of protesters unfurled a large banner in the colours of the German flag, bearing the words: "Angela, don't cry, there isn't a crumb of bread in the cupboard."
Opposition parties, labour unions and communist-affiliated group Pame are planning to greet the German leader with street protests and work stoppages on Tuesday.
The leader of nationalist party Independent Greeks, Panos Kammenos, has also called for a gathering and plans to deliver a message of protest to the German embassy.
The visit comes at a crucial time for the heavily indebted country, which is locked in negotiations with its international creditors over a 13.5-billion-euro ($17.5 billion) package of cuts.
A positive outcome is vital to unblock a 31.5-billion-euro installment from Greece's EU-IMF bailout package, which is needed to recapitalise banks and repay outstanding domestic debts in a country that is heading for a sixth straight year of recession.