A taxi driver needed hospital treatment after being attacked and robbed.
He took a fare into Bushby Close, Lancing, when the male passenger assaulted him with an unknown instrument, causing serious facial injuries.
The attacker made off with the taxi driver's money bag.
The driver was treated at Worthing Hospital.
Detective Constable Gary Tattersall said: "This was a vicious attack in an area which is well-used. The attacker must be caught."
The man was described as white, in his 20s, 5ft 9in to 5ft 10in, with short brown hair. He was wearing dark clothing.
The incident happened on Thursday at 3am. Anyone with information should call 0845 6070999 ext 81244.
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