A coastguard rescue operation was launched on Sunday evening after an aircraft emergency locator beacon was activated from an area of the North Sea.
When an aircraft beacon is activated, it allows search and rescue teams to locate a plane and survivors who may be in distress and in need of immediate rescue. In response to the alert at 9.30pm, the coastguard sent out a plane and a helicopter.
The RNLI also sent out lifeboats from the Humber and Cromer. Radio conversations suggested the teams were looking for a person in the water and debris.
Read more: School pupils demand repairs to Grimsby playpark as petition handed over to council
However, after hours of searching and doing parallel tracks over the North Sea, teams found "nothing untoward". The rescue teams have since stood down, as mystery surrounds the emergency beacon.
A spokesperson for HM Coastguard said: "HM Coastguard was alerted to an aircraft emergency locator beacon activation just after 21:30 last night (9 July) approximately 60 nautical miles North East of Cromer.
"A Coastguard helicopter, coastguard fixed wing aircraft, RNLI lifeboats from Cromer and Humber, and a vessel in the area were all sent. A thorough and extensive search was carried out alongside further investigations and nothing untoward was found.
A spokesperson for the Humber RNLI said: "RNLI all-weather lifeboats from Humber and Cromer were involved in a search co-ordinated by HM Coastguard. Both lifeboats have now been stood down."
