According to Sussex Police, officers were called to Montague Street at around 12.40am this morning (July 13) by two men who said they had been approached and threatened by a man holding what appeared to be a gun.
The man used the object to assault the two men, police said, causing facial injuries that required hospital treatment.
Police have described the man as black, in his late 30s, with a short beard and short black hair, wearing black jogging bottoms gathered at the bottom, a grey hooded jumper and trainers.
He was riding a blue mountain bike, police added.
He was reported to be in the company of a second man, described by police as white, around 40 years old, unshaven and wearing a grey hooded jumper and jogging bottoms also gathered at the bottom.
He was riding a purple bicycle, police added.
Police said officers also received reports of a third man being assaulted and robbed by the same suspect, but have been unable to make contact with the alleged victim.
A suspect was arrested in Brighton Road in Worthing by police using a Taser. He was arrested on suspicion of robbery and remains in police custody, police said.
Officers are keen to hear from anyone who witnessed the incident, or who saw men matching either description in the area at the time. They are also keen to hear from any other victims.
Anyone with any information is asked to contact police online or by calling 101 quoting Operation Duffield.
Alternatively, you can contact the independent charity Crimestoppers anonymously on 0800 555 111.