It is feared all eight on board - seven Poles and one Philipino - are dead

The ship is no longer visible after sinking below the surface

Eight people were on board the Cypriot-

A cargo ship found overturned off the Scottish coast has sunk below the water's surface as coastguard rescue teams continue searching for the eight missing crew members feared dead.

While lifeboats involved in the search effort have been stood down, air and coastal searches are continuing.

The operation was mounted after the upturned hull of the Cypriot-registered Cemfjord was spotted in the waters of the Pentland Firth, north of Scotland.

This afternoon a spokeswoman for the Maritime and Coastguard Agency (MCA) said the vessel was no longer visible after having submerged below the water's surface.

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A major air and sea rescue operation was mounted after the overturned hull, above, was spotted yesterday

The search operation was called off last night after dark. A tug boat remained behind to illuminate the scene

But she said 'sadly' there had not been any sign of the missing crew, made up of seven Poles and one Filipino.

Two helicopters, four lifeboats and five coastguard rescue teams had this morning resumed the search for the eight people who were on Cemfjord.

A spokesperson for the Maritime and Coastguard Agency (MCA) said 'every effort' was being made to find them.

The search was sparked after the crew of a passenger ferry raised the alarm when they spotted the upturned hull of the vessel in the Pentland Firth, north of Scotland.

After darkness fell last night it was called off, although passing vessels were asked to scan the area.

The MCA spokesperson said: 'The search has resumed this morning, with two helicopters, four lifeboats and five coastguard rescue teams. There is no sign of any of the crewmen.

'It is early in the day so we will see how the day progresses, but every effort is under way.'

German shipping company Brise of Hamburg confirmed yesterday that there were eight people on the ship, seven Poles and one Filipino, adding that there had been no distress call.

The Cemfjord was drifting at 5.2 knots, roughly 6 mph, according to readings recorded yesterday

The RNLI searched a large area of ocean, marked in blue, looking for survivors from the sinking vessel

The 83-metre bulk cement carrier had been bound for Runcorn, Cheshire, on the west coast of Britain.

Shetland Coastguard was alerted by the NorthLink ferry Hrossey which spotted the vessel around 10 miles east of the Pentland Skerries, about 15 miles from Wick.

Passenger Caitlin Ditchfield told the BBC: 'After a while the captain made an announcement that he had called the three closest coastguards but they had asked that the ferry conduct a search while the lifeboats made their way to us.

'The ferry started to circle the ship looking for any debris. We were at the scene for two-and-a-half hours before the coastguards said we could carry on with our journey.'

The Cypriot-registered Cemfjord, a cargo ship carrying cement, pictured, was last seen Friday afternoon

She said it had been a rough crossing but conditions were decent when they spotted the overturned vessel.

A spokesman for Brise of Hamburg said yesterday that the 'crew of eight are missing following a severe accident in the Pentland Firth, off the north of Scotland on Friday January 2'.

The statement said: 'The crew consists of seven Polish seafarers and one Filipino mariner. The company is in the process of informing the families.'

An MCA statement said: 'The search has begun again this morning for eight crew missing from the cement carrier Cemfjord, which capsized and sank in the Pentland Firth.

'The two helicopters and four lifeboats have resumed their search and will be joined by coastguard rescue teams from Kirkwall, St Margaret's Hope, Duncansby, Scrabster and Wick. HMS Somerset and her helicopter have also joined the search.

The crew of Northlink ferry Hrossey, pictured, reported that there were no survivors in the immediate area

'The search has been ongoing since 2.30pm yesterday afternoon when the vessel was found capsized by a passing ferry. Sadly no sign has yet been found of the missing crew.'

Last night a spokesman for the MCA said it 'was not looking particularly encouraging' that the crew would be found.

The search last night was co-ordinated by Shetland coastguards. Four RNLI lifeboats from Wick, Thurso, Longhope and Stromness were sent to the area.

The coastguard rescue helicopter from Shetland and an RAF rescue helicopter were also scrambled. As darkness fell, other vessels in the area joined in the hunt.

A Maltese registered tug, the Herakles, remained on station last night illuminating the area and warning other shipping about the danger posed by the semi-submerged cargo ship.

The Cemfjord was drifting at 5.2 knots, roughly 6 mph, according to readings on marinetraffic.com that were recorded yesterday. It left port in Aalborg, Denmark on December 30.

The Pentland Firth is a channel between the north tip of Scotland and Orkney that is known for strong tides and requires careful planning to sail, according to Sail North Scotland.

Eight people were on board the vessel, pictured partially-submerged in the sea