A search and rescue mission is taking place off the coast of Essex.
The Coastguard is leading the operation, with RNLI boats also said to have been in attendance.
East of England Ambulance Service said it is not aware of any incidents in the area where patients may have been brought ashore at present.
A Coastguard helicopter from Lydd and a plane were sent to the incident, according to the Maritime and Coastguard Agency.
A spokesperson added: “HM Coastguard has been coordinating a search and rescue response to an incident off Essex, working with Border Force and other partners.
“HM Coastguard will continue to safeguard life around the seas and coastal areas of the UK, working with search and rescue resources in the area.
“If a vessel needs search and rescue assistance, HM Coastguard will continue to respond and rescue those in danger.”
A Home Office spokesman said the department would provide further details after the initial response once the situation had been resolved.
Essex Police confirmed Border Force are leading the investigation and did not comment further on the incident.