An empty life-raft was found today by search teams hunting for a missing fishing trawler.
The Meridian and its four crewmen disappeared in the North Sea last night during violent storms.
A major search involving military aircraft from Scotland and Norway was launched overnight after the alarm was raised.
The RAF revealed today that an empty life-raft had been found in the sea, along with items like buckets and survival equipment.
Rescuers said they hoped the crew were safe in the trawler's second life-raft as fears grew.
The missing boat was registered in Kirkcaldy in Fife and was based in the nearby fishing village of Anstruther. Three of the crew are from Anstruther while the fourth is from Aberdeen.
The alarm was raised when staff at the RAF rescue centre at Kinloss in Scotland picked up a distress beacon late last night.
An RAF Nimrod search and rescue aircraft was involved in the search, 160 miles east of Aberdeen on the boundary line with the Norwegian sector of the North Sea.
The search is being co-ordinated by the Norwegian coastguard in Stavanger who are liaising with the UK coastguard at Aberdeen.
A number of fishing boats and a second Sea King from RAF Boulmer in Northumberland were assisting in the search.
RAF spokesman Michael Mulford said: "The beacon was found at 2.20am, the life-raft at 2.30am and some debris at 3am.
"We believe they had one other life-raft so all hope now has to rest upon that.
"We're now many hours down the line. No one could survive in the water that long. If they are in another life-raft, conditions will have been extremely difficult.
"As it's the Norwegians' patch it's up to them now whether to continue the search or not. It's a heart-break decision, but at some point they will have to make it."
Borghild Eldoen, of the Joint Rescue Co-ordination Centre for southern Norway, said: "We will keep searching until something else has been decided."
Flight Lieutenant Rick Riley, captain of the Nimrod involved in the search operation overnight, said the Norwegian helicopter had spotted some debris in the water, but on further inspection had found "nothing untoward".
He said his aircraft had scoured the area for seven hours but had not seen any sign of the vessel.
"Initially we took up a co-ordinating role, which involved setting up two fishing vessels and a couple of rig support vessels to search the area," he said.
"We then did a visual lookout with search lights but it was dark at the time and the weather was very rough, which made it difficult to see anything in the water."
He added that their radar which locates all vessels in the area had failed to locate the trawler.
First pilot Flight Lieutenant Alex Sell said: "We obviously gave it our best efforts and these are continuing.
"There is always hope. When we left, the weather was improving and we are using everything that is available to us."
Bertie Armstrong, chief executive of the Scottish Fishermen's Federation, said: "We're all sitting on our hands desperately waiting for news while the full might of maritime search and rescue is applied.
"There's absolutely no doubt that we have an extremely serious situation here. If a boat has been missing for this number of hours in such horrendous conditions, the outlook is bleak. It would be daft to say otherwise."
Scott McAuslan, 31, who lives near the harbour area in Anstruther, said the news had shocked the town.
He said: "I hope they do find them but I think they've been looking for the boat for a while now.
"It's a really small town, the type of place where people know each other, so it's something that will affect people."
Ian McGlashan, 61, of East Green in the town, said: "It's a terrible thing. Everyone I've been speaking to has asked if there's any news about it.
"The fishing and harbour are really important to the town so it's something that people will care about.
"The families must be in a real state, not knowing what is happening."
Susan Shaw, 44, who also lives in the town, said: "I just hope they manage to find them somehow. It's a terrible thing but I suppose there is always that danger at sea."
The harbour master's office on the town's seafront was the main focus of activity today, but officials were declining to comment.