According to early estimates broadcast on public television, the Social Democrats remained the strongest party but lost four percentage points on their 2003 result to land at about 38 percent.
Voters also shaved four points off Chancellor Angela Merkel's conservative Christian Democrats (CDU) result four years ago to give them around 25 percent.
The SPD, led by Mayor Jens Böhrnsen has governed for the past 12 years in Bremen with Chancellor Angela Merkel's CDU in a "grand coalition" that mirrors her federal one in Berlin.
Greens, Left Party the real winners
Meanwhile the opposition Greens made a strong showing at 16.5 percent -- making them a potential coalition partner in the smallest of Germany's 16 states. The party is not represented in a single state parliament and was voted out at the national level in September 2005.