A 21-year-old woman who had climbed onto the roof of a town hall in Germany to commit suicide inadvertently caused a mass punch-up among a crowd that had gathered below after a group of young men started urging her to jump.

Six police officers were injured when they intervened to stop fighting between youths and a group of homeless men in the southern town of Lörrach as the hapless woman watched from above.

"Among the many onlookers were several young men who in the past have come to attention for being violent and criminal," the Lörrach police said in a statement. "These people were jeering and urging the woman, as unbelievable as this may sound, to jump."

"A nearby group of homeless people heard what they were saying and started hurling abuse at the shouters," police said. A wild punch-up involving 40 people ensued and the local police had to summon help from other police forces to contain the violence.

Meanwhile up on the roof, negotiators held tense talks with the woman and managed to persuade her not to jump. She came off the roof after three and a half hours and is receiving counselling.

Police have asked eyewitnesses to come forward to help with their investigation. "The chief of police utterly condemns the rioters' behavior and will continue to operate a zero tolerance policy," the statement said.