A man arrested for serious sexual assault and put in handcuffs has escaped police custody in far north Queensland while being transferred to a watchhouse outside Cairns.

The 25-year-old man was arrested on Saturday afternoon and was being taken to Ravenshoe Police Station where he was to be placed in a secure vehicle for transfer to the Mareeba Watchhouse.

But as that changeover was taking place at about 1.45pm on Saturday he fled from police into nearby bushland.

Officers chased the handcuffed suspect and set up cordons as the dog squad attempted to track him down.

But heavy rain slowed the search and he had not been found late on Saturday.

He has not been named by police but is described as being Caucasian, 175 centimetres tall, and wearing bright yellow shorts, a green and grey t-shirt and handcuffs.

Members of the public are urged not to approach him and to call police immediately.