Tuilagi, 20, swam to a nearby pier at the Auckland Ferry Terminal where he was met by police at 6.48am BST and taken to Auckland Central Police station.
The Leicester centre was given a pre-charge warning for disorderly behaviour before being released back to the England team management, who were said to have been "a little bit embarrassed".
Noreen Hegarty, a spokeswoman for the Auckland police, would not confirm the identity of the player but it is believed it to be Tuilagi.
Ms Hegarty said: "A member of the England rugby team at 6.48pm yesterday (New Zealand time) jumped overboard from a ferry just before it was about to berth at the ferry terminal in Auckland and he swam to a nearby pier.
"He was then detained by police and given a pre-charge warning for disorderly behaviour and he was collected by his team management."
It has been reported that Tuilagi was returning from a day trip with to Waiheke Island with fellow England team-mates.
Tuilagi was England's most impressive player in their 19-12 World Cup quarter-final defeat to France at Auckland's Eden Park on Saturday.
Neither the police nor the Rugby Football Union would confirm whether Tuilagi was drunk at the time he jumped from the ferry.
The RFU said a statement would be issued in due course.
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