Rescue teams are expected to resume the search for two RAF airmen who went missing after two Tornado jets crashed off the north coast of Scotland, the Ministry of Defence said.
Four personnel from RAF Lossiemouth were involved in the incident on Tuesday, in which the Tornado GR4s came down in the Moray Firth yesterday.
A rescue helicopter picked up two people who were taken to hospital in Inverness, before continuing to search for the remaining pair.
Aberdeen coastguard contacted the RNLI for assistance at around 1.50pm on Tuesday after reports that the jets came down about 25 miles south of Wick.
About 15 lifeboat volunteers joined the rescue operation in boats from Wick, Invergordon and Buckie, the RNLI said.
The boats headed for the Beatrice oil field area, supported by a helicopter from Stornoway in the Western Isles.
Crew from the Buckie boat reported that two people were taken from the sea by helicopter and flown to Raigmore Hospital, although their condition is not known.
Group Captain Ian Gale, the station commander, said his thoughts were with the families and friends of those involved.
"It is with great regret that I must confirm the loss of two Tornado GR4 aircraft, from this station, in an incident in the Moray Firth today," he said in a statement released by the Ministry of Defence (MoD).
"The circumstances remain uncertain but clearly this is a very serious incident.
"This incident involved four aircrew, all personnel from this station, and the thoughts of everyone here are with the families and friend of those involved."
He would not comment on the aircrews' condition or the circumstances of the incident.
"I can confirm that two individuals have been recovered and two remain unaccounted for," he added.
"I am confident that the Tornado aircraft on this station are operated as safely as they possibly can be - however, today's incident is a stark reminder that the military operations and training we conduct are not without risk.
"What happened today is under investigation and more details will be released by the Royal Air Force in due course.
First Minister Alex Salmond said: "This is clearly a very serious incident and my thoughts are with the loved ones of those affected.
Moray MP Angus Robertson, the SNP's defence spokesman, said: "My first thoughts are with the crew, their families and colleagues.
"Everyone in Moray has a connection with the RAF and this incident will be felt right across the community.
"The priority must now be for the support of the affected families and for the authorities to investigate the causes of this incident and ensure the future safety of flying operations and personnel."
Tornado aircraft have been involved in crashes in Scotland in recent years.
In January last year two RAF crew were rescued after their Tornado GR4 jet came down in the sea off the west coast of Scotland.
The crew, from RAF Lossiemouth, ejected from the plane before it landed in the waters at Loch Ewe, near Gairloch, Wester Ross.
RAF Lossiemouth, on the Moray Firth coast, is home to three squadrons of Tornado GR4s.
The Tornado GR4 is a two-seat attack aircraft, capable of delivering a variety of weapons and reaching a maximum altitude of 50,000ft (15,240m).
In July 2009 an RAF pilot and navigator were killed when their Tornado jet crashed into a hillside in Argyll.
Flight Lieutenant Kenneth Thompson, 27, and Flight Lieutenant Nigel Morton, 43, died in the crash near the village of Arrochar.
The aircraft was a RAF Leuchars-based Tornado F3 on a routine flight.