A woman is in a life-threatening condition in hospital after an assailant poured a liquid over her on a tram in eastern Germany and set her alight.

Police said no-one else was injured in the incident in Gera on Sunday, German news agency dpa reported.

Passengers stopped the tram by pressing an emergency button, and the assailant took the opportunity to flee.

The incident occurred in Gera, eastern Germany, on Sunday (Bodo Schackow/dpa/AP)

The tram driver immediately began to extinguish the flames, and the 46-year-old woman was taken to hospital by helicopter.

Police are hunting the assailant.

It is not yet known what prompted the attack, or what the liquid was.