An armed man walked into a Worthing betting shop yesterday evening and threatened staff with a handgun.
Police are investigating the robbery - the second in recent weeks - which took place at 7pm on Sunday.
A Sussex Police spokesman said: "A man went into the Ladbrokes in Broadwater Street East, Worthing, carrying a handgun and demanded cash from the members of staff.
"He left with a quantity of cash and the staff were unharmed.
"The suspect was wearing a grey top and grey jogging bottoms and had his face covered."
Anyone who saw a man in the area in the area acting suspiciously is asked to contact police online quoting serial 1003 of 12/05.
This is the second branch of Ladbrokes to be targeted in a robbery in recent weeks.
On April 24, the Rowlands Road branch in town was robbed by a suspect armed with a knife, police said at the time.
The police helicopter was called out to assist with the search following an initial call to police at around 5.50pm.
Sussex Police say they are not currently linking two incidents.