Two people are understood to have been rescued from the sea off the Essex coast.
Border Force officers and RNLI lifeboat crews responded to an incident near the port town of Harwich on Monday in an operation co-ordinated by the Coastguard.
A source with knowledge of the search and rescue operation told the PA news agency two people have been rescued and it is understood a dinghy has been recovered.
It is feared more people may be unaccounted for but this has yet to be confirmed.
Harwich lifeboat launched at 4.05pm on Monday, returned and then launched again at 11.35pm, before going back to shore at 8am on Tuesday. Searches have since ceased.
The RNLI said: “RNLI lifeboats from Harwich and Walton and Frinton were involved in a search and rescue operation to a suspected person in the water.
“All have been stood down by HM Coastguard, who are continuing to co-ordinate the search with Border Force.”
The Maritime and Coastguard Agency said a Coastguard helicopter and a plane were sent to the incident, adding: “HM Coastguard has been co-ordinating a search and rescue response to an incident off Essex, working with Border Force and other partners.”
The Home Office confirmed that Border Force and the Coastguard were working on a co-ordinated search and rescue operation after an incident on Monday.
More information will be provided after the initial response and once the situation has been resolved, a department spokesman added.