The protesting municipal workers pushed and threw coffee on a German consul in Thessaloniki, Wolfgang Hoelsche-Obermaier, who arrived to attend a conference of Greek and German mayors being held in the city. They later forced open shutters and entered the conference centre, where they clashed with riot police.
A German deputy labour minister who has been appointed special envoy to Greece, Hans-Joachim Fuchtel, was also attending the event.
"These people haven't come here to help us, but to announce our death sentence," said Themis Balasopoulos, leader of Greece's municipal workers union, who was at Thursday's demonstration.
The protesters chanted "Nazis out" and "This will not pass" as they tried to obstruct municipal officials from attending the conference.
Hoelsche-Obermaier said he was not upset by the attack against him.
"It was a misunderstanding. I am more pro-Greek than I was before today," he told reporters.
Germany is the biggest contributor to Greece's rescue loans and has been one of the most vocal advocates of the tough austerity measures demanded of Athens. As a result, protesters in Greece often target Germany in their demonstrations.
Last month, around 50,000 people demonstrated in Athens when German Chancellor Angela Merkel paid here first official visit to Greece since the country's massive debt crisis broke out. She expressed support for the conservative-led government's efforts to limit high budget deficits.
The Greek Parliament last week passed a new austerity package that bailout creditors had demanded in exchange for paying out more rescue loans. The package raised the retirement age and cut pensions and raised taxes. It has also has eased restrictions on firing workers.
In a chaotic scene on Thursday, riot police chased protesters through the conference centre complex from building to building. There were no immediate reports of arrests.
The protesters played Nazi anthems over loud speakers, as well as Greek radio recordings from World War Two.
Left-wing German lawmaker Annette Groth joined the protesters outside the conference centre, where clashes with riot police also occurred.
"I have also been unemployed," she told the crowd. "It is not you who should pay the price for this crisis but the rich."