One vehicle was involved in the incident at 23:30, which happened outside Crabby Jacks near the Rue de Goddards Junction.
Five people were in the vehicle at the time; two suffered serious injuries, two were treated for minor injuries and one man has died.
In a statement, Bailiwick Law Enforcement said the name of the deceased will not be released until all family members have been notified of the tragic news.
Investigations are continuing into what happened and specialist collision experts have been sent to the scene.
Anyone who heard or witnessed what happened is asked to contact Guernsey Police on 725111 and ask for either Inspector Tom Marshall or PC James De La Mare.