No one has been found so far and police want to find what happened so they can find out if the person is OK.
Police received a report of someone jumping into the river from a bridge in Princes Drive, Leamington, at 1.54am.
The fire brigade also attended and carried out a search of the river but were unable to find anyone.
Inspector Rich Hobbs said: “It is vital we establish whether anyone has entered the water and if so we need to check on their welfare. If anyone has information that could help with our enquiries then please get in touch.
“If you are the person who jumped in the river please get in touch to let us know you are safe and well so we can stand down our investigation.”
Anyone with information can call police on 101 quoting incident 50 of 15 May 2022.