Two masked robbers forced a woman's car to a halt before robbing her of a gold necklace.
The 56-year-old victim was targeted in Evington, Leicester, shortly after 10pm on Wednesday as she drove home from work.
A dark-coloured car overtook as she drove along Headland Road towards the junction with Ethel Road.
It pulled up in front of her, forcing her to stop. The driver and passenger got out and walked towards her and told her to hand over her jewellery.
The victim locked her car but the men then smashed the driver's side window and the woman handed them her gold necklace.
The robbers also took her car keys before they went back to their vehicle and drove away.
A witness, who was driving past at the time, said: "I thought it was a fight or maybe a car crash.
"The men got out of their car and I assumed it was to swap insurance details.
"But they began smashing the car window and I saw there was a lady in the car.
"One of the men reached in and I think he grabbed a chain from around her neck. The lady was distraught, but as far as I could tell she wasn't hurt.
"The men were very professional about it. It didn't look random to me.
"They left the house that night intending to do what they did. It was shocking."
Residents said they initially thought there had been an accident.
Anil Bhima, 36, said: "You have to ask how they knew she had gold jewellery. On a dark night you wouldn't be able to see it.
"They must have followed her and then seen the chance to stop her car here.
"They smashed the window very quickly. I don't know what they used but it's difficult to do that. It was all very quick and professional. It's very frightening that a woman could be attacked like this. This is a quiet area."
Police last night appealed for help tracing the men.
Detective Constable Charlotte Mee said: "This was a frightening incident for the victim, which has left her extremely distressed and we need to catch those responsible.
"If you were in the Headland Road area and saw any part of the incident, please contact us immediately.
"We would also like to speak to anyone who has heard rumours locally about who may have been involved in this incident. Any information you can provide may help us with our inquiries."
One of the men is thought to be Asian. He is in his mid 20s, 6ft and of medium build. He was wearing dark clothing and half of his face was covered with a dark cloth.
The second man is also in his mid 20s and of medium build. He was wearing dark clothing.
Contact Det Con Mee on 101 or Crimestoppers on 0800 555 111.
