Neighbours of the 25-year-old man in the eastern Berlin suburb of Hellersdorf called in officers to investigate as he appeared to have an endless supply of fireworks, police said.
Some of the "explosions from his fireworks were so strong that windows were vibrating," police said in a statement.
Police did not find the man when they descended on his apartment, but found that his cellar was packed with fireworks.
Investigators later found that he had apparently also rented a second cellar space in the building.
In all, the man allegedly hoarded "around one tonne of legal as well as illegal pyrotechnics", police said.
Police are now investigating if he violated rules on explosives.
Firecrackers and rockets are an essential part of New Year s festivities in Germany, with individuals firing off large amounts of pyrotechnics from balconies or their lawns.
They are sold on the last three days of the year. Sales in 2014 were worth 129 million euros ($140 million).