A pregnant woman was left beaten and bruised outside Watford Junction station after being assaulted in her car on Wednesday.
The 26-year-old from Buckinghamshire was attacked in the face and stomach by a woman who pulled open the victim's car door in the station's bus stop area.
The incident took place shortly after 5pm.
The offender is described as a black woman with her hair tied back, wearing dark clothing and trainers, and carrying holdalls or bags over her shoulder.
PC Dean Woodgate, said: “This was a nasty incident where the victim received some bruising.
“I would really encourage anyone who has any information or who can identify the offender to come forward.”
Anyone with any information is asked to telephone 0845 33 00 222 or 0800 555111.