A dog walker found a military shell on the beach at Seaton Carew as an army bomb disposal unit was called out to carry out a controlled explosion.
The drama took place in Seaton on Sunday morning.
Cleveland Police say a dog walker got in touch at 8.30am to report he had found what looked like a military shell.
Back-up was called in, and a controlled explosion was carried out on the sand dunes at lunchtime.
A Cleveland Police spokesman said: "We were contacted by a dog walker at 8.30am on Sunday, reporting he had found what looked like a military shell on the beach at Seaton Carew.
"Police contacted our Ministry of Defence (MOD) colleagues who sent explosives ordnance device (EOD) experts, and they arrived on scene at 10.30am.
"The item was X-rayed and it was decided to carry out a controlled explosion on the sand dunes.
"This took place just after midday."
The shell which was found is thought to date back to the Second World War.
After the controlled explosion, the area was made safe again for the public before being reopened.
While the incident was ongoing, a statement from Hartlepool Neighbourhood Police Team, posted on its Facebook page, said: “A controlled explosion will take place.
“Thank you for your patience whilst the area is made safe.”