Police were called to Franses jewellers on Westover Road, Bournemouth, after reports two men entered the store and threatened staff with handguns at about 16:30 GMT.
An unknown quantity of items were stolen before the pair made off in a black Ford Fiesta, officers said.
Two men, both aged 24, and a 30-year-old woman were arrested on suspicion of robbery.
The vehicle was later recovered on the A338 Spur Road near to the Blackwater Junction.
Det Insp Andy Bell said: "I would also like to hear from anyone who saw a black Ford Focus with registration number BG05 OJU being driven between Westover Road and the A338 Blackwater Junction."
Staff were threatened during an armed raid at a jewellers.