Two men threatened and demanded cash from a taxi driver after waving down his car in Batley.
At around 9.45pm on Tuesday, a taxi-driver arrived at Abbey Road in Healey to collect a fare, but the house he was called to was in darkness.
The driver turned his taxi around in a cul-de-sac and began to drive off but was waved down by two men who approached the car from the Spen Valley Greenway.
They got into the taxi and threatened the driver, pressing a metal implement against his face.
The suspects demanded cash but the driver pressed his horn and they ran off towards Fountains Avenue.
The taxi driver was not harmed.
Both suspects were white. One man was in his late teens, around 5ft 10ins tall with a slim build and wore trousers and a t-shirt.
The second suspect wore a dark coloured balaclava.
Enquiries are ongoing. Witnesses can contacted Det Con Peter Usher at Kirklees CID via 101.