Coastguard search teams and volunteer crews with the RNLI’s all-weather and inshore lifeboats are involved in the operation.
The Coastguard helicopter has also been called in.
The search is concentrated in the area around Steetley Pier.
A Maritime and Coastguard Agency spokesperson said tonight: “At approximately 6.15pm today, Thursday, July 15, HM Coastguard received multiple 999 calls from members of the public concerned about a person in the water off Steetley Pier in Hartlepool
"Hartlepool Coastguard Rescue Team and RNLI lifeboats were sent, alongside the search and rescue helicopter from Humberside and Cleveland Police, to conduct a search.
"The search is ongoing.”