Eight other people were treated for non-life-threatening injuries.
A man in his 40s was arrested on suspicion of manslaughter.
An investigation was launched into the incident, which is not clear how the two sustained their critical injuries.
The beach was cleared and a cordon was set up.
Dorset Police is working with the Marine Accident Investigation Branch and the Maritime and Coastguard Agency.
Anyone with information is asked to contact the police.
LONDON DAILY ARCHIVE
Dorset Police Investigates Deadly Incident at Bournemouth Pier
A 12-year-old girl and a 17-year-old boy died after being pulled from the sea off Bournemouth Pier.
31 May 2023 · 22:40 UTC
