The violence erupted as an Eritrean cultural festival was set to begin in the city of Stuttgart on Saturday.
The festival was organised by supporters of the Eritrean regime loyal to Eritrean President Isaias Afwerki.
Police sent to the scene found themselves caught in “massive violence” between the two opposing groups, the deputy police commissioner said.
“Neither the extent nor the intensity of the violence was apparent in advance,” Carsten Hoefler said in a statement on Saturday.
Officers were attacked with bats, nails, metal rods, bottles and stones, the statement added.
Six officers were admitted to hospital, while 228 people were arrested.
The violence has been condemned by officials in the city.
“We must take decisive action against the emergence of conflicts from other states on German soil,” said Stuttgart Mayor Frank Nopper, according to German news agency dpa.
The chaos follows a string of similar recent protests. As Eritrea marks 30 years of independence from Ethiopia, festivals have been held by members of its diaspora in recent months, with many ending in conflict.
Eritrea, one of the poorest countries in Africa, is a one-party state with a repressive and highly-militarised society. The UN estimates that hundreds of thousands of Eritreans have fled the country.
Reporters Without Borders has rated Eritrea as having the worst overall press freedom in the world, even lower than North Korea, with all publications and access heavily controlled by the government.
In August, a protest broke out after a cultural event in Stockholm, Sweden, where more than 50 people were injured and festival tents and booths were sent on fire.
In July, German police used batons and pepper spray to quell crowds targeting an Eritrean musical festival after opposition supporters called the event “an exercise in Eritrean government propaganda”.
Earlier this month, Israeli president Benjamin Netanyahu announced plans to deport Eritrean asylum seekers involved in riots in Tel Aviv.
Stun grenades, tear gas and sponge-tipped bullets were used by Israeli police against hundreds of Eritrean regime opposers on 3 September, following a cultural festival.
Last month, a three-day Eritrean cultural festival in Toronto, Canada, was cancelled after supporters and opponents of Eritrea’s regime clashed.