An assessment is being made on whether to resume the search for two airmen missing in the Moray Firth after two RAF Tornado jets crashed.
Operations were suspended on Tuesday evening after the jets are understood to have collided.
The Tornado GR4s, which each have a crew of two, were from RAF Lossiemouth, in the north east of Scotland.
Two of the four air crew were airlifted to hospital in Inverness but there are no details about their condition.
The Ministry of Defence said it was making an assessment on when it can resume its search. Visibility was said to be poor in the area.
Police and the Coastguard have been patrolling shorelines and members of the public have been asked to report any debris.
Aberdeen Coastguard was alerted to the incident at about 13:50 BST on Tuesday, after reports that the jets came down about 25 miles south of Wick.
The RNLI said 15 volunteers manned the Wick, Invergordon and Buckie lifeboats, which were used to search for the missing personnel.
The boats headed for the Beatrice oil field area, supported by a helicopter from Stornoway in the Western Isles.
Wreckage from one of the aircraft was collected from the water and transported back to shore on lifeboat Buckie - the location of the second aircraft is not yet known.
Lossiemouth station commander Gp Capt Ian Gale said: "The circumstances remain uncertain, but clearly this is a very serious incident.
"The thoughts from everyone here are with the families and friends of those involved."
First Minister Alex Salmond said: "This is clearly a very serious incident and my thoughts are with the loved ones of those affected.
"I understand rescue services have done all they can to help with the situation and offer my thanks to all those involved.
There have been previous accidents involving RAF Tornado aircraft.
In January 2011, an engine fire caused a Tornado GR4 based at RAF Lossiemouth to crash into the sea off north west Scotland - the crew in that incident managed to eject to safety.
The following month, a Tornado crew was forced to eject after experiencing problems landing at the same base - there were not thought to have been serious injuries.
The supersonic Tornado GR4 attack aircraft has seen decades of RAF service, being used in various military operations that include in Iraq, Kosovo, Afghanistan and most recently Libya.
Video: Wreckage of crashed Tornado