A suitcase exploded and caught fire near a refugee registration centre in the northern Bavarian town of Zirndorf on Wednesday, but no one was injured in the incident, police said.
Explosives experts and police were examining the suitcase, which may have been filled with aerosol cans, police said in a statement.
Police said they were searching the perimeter for two people of interest - a man aged about 30 and a woman aged about 25.
Both were seen by witnesses pulling suitcases with them.
Two terrorist attacks claimed by Islamic State and one mass shooting by a German-Iranian teenager in Munich - all carried out over the past week in southern Germany - have left the country shaken.