An operation to refloat a stricken cargo ship which ran aground in rough seas, sparking the rescue of seven crew members, is due to begin today.

Salvage and counter pollution experts will this morning begin assessing the damage to the 82-metre long vessel after it hit rocks near Colwyn Bay in North Wales.

The Marine and Coastguard Agency (MCA) said the cargo ship was in one piece following yesterday's incident, but there are growing concerns that it could begin to leak some of the 40,000 litres of fuel it is carrying.

Two lifeboats and a Royal Navy and RAF helicopter were involved in the dramatic rescue of the seven Polish crew members after their vessel got into difficulties as the Welsh coast was battered by Gale Force Nine winds and five metre swells.

Five of the seamen were rescued by a Royal Navy Sea King rescue helicopter scrambled from RNAS Prestwick.

But the aircraft developed a problem with its winch wire, forcing rescue co-ordinators to send out a second helicopter from RAF Leconfield to collect the remaining two crew members.

An MCA spokeswoman said: "At 8.15pm last night Liverpool Coastguard received a distress call from the cargo ship 'Carrier' telling them they had run aground at Raynes Jetty, Llanddulas.

"A strong gale was blowing and a five metre swell was reported. Because of the location of the grounding Holyhead Coastguard coordinated the rescue. All seven of the Polish crew were taken uninjured from the ship by two rescue helicopters. The first from RNAS Prestwick, the second from RAF Leconfield."

The Welsh Government said it was "closely monitoring" the situation and being kept fully informed of developments.

During the five-hour long operation the A55 was closed to allow emergency workers safe access to the vessel.

All-weather lifeboats from Llandudno and Rhyl were also launched at 8.30pm to offer assistance to the rescued crew, the MCA said.

Eyewitness Sophie Madeley, who watched the rescue from the A55, said the rescue teams had done an "amazing" job.

She told the BBC: "I have watched this all night, my high respect goes out to the pilot of the helicopter for the amazing work I watched him do, and also out to the crew for battling it through what has happened."

The ship, which is registered in Antigua and Barbuda and was carrying a cargo of stones, is now resting against concrete dolosse blocks on the beach at Llanddulas, which runs adjacent to the A55.

Members of the coastguard, North Wales Fire and Rescue Service, ambulance and police service remained at the scene overnight along with North Wales Trunk Road Agency officers.

The MCA said the reason for the ship running aground was not yet clear.

"Salvage and counter pollution experts will be on site in the morning," added the spokeswoman.

The crew had been taken by ambulance to North Wales Police headquarters in Colwyn Bay where they were given hot drinks and a change of clothes and transported to a nearby hotel, said North Wales Police.

A spokeswoman said: "The ship is still insecure and the A55 remains closed in both directions and an assessment of the situation will be carried out at first light. The weather remains difficult with high winds and rough seas."

Assistant Chief Constable Gareth Pritchard added: "This was a very difficult operation involving many agencies in very bad weather. Everyone is delighted that the seven crew men were rescued without injury and they are safe and well."

The Royal Navy Sea King helicopter from HMS Gannet in Prestwick, Ayrshire, was first on the scene.

A Royal Navy spokeswoman said the crew were forced to leave one aircrewman on board the stricken boat following a problem with the rescue helicopter's winch.

The team rescued five stranded crew members before the aircraft developed a defect and Petty Officer Mike Henson was left on board with two remaining seamen.

All three were later rescued by an RAF helicopter.

It was Petty Officer Henson's first shift as a qualified search and rescue aircrewman.

HMS Gannet's duty observer, Lieutenant Angela Lewis said: "Conditions were extremely challenging.

"Sea spray from the waves was being whipped up to a height of about 60ft in places and we were in the hover at about 80ft, so it was quite nerve-wracking.

"We put Petty Officer Mike 'H' Henson down on the deck of the vessel and he then quickly packaged the first four members of the crew in separate winches.

"We dropped them off on the A55 to a waiting ambulance and returned for the remaining three crew and our Winchman. Unfortunately we were only able to complete one lift on this second run before the winch was damaged."

An MCA spokesman added that a "quantity" of marine gas oil has leaked from the boat.

There are three holes in the starboard side, but the port side - where the fuel tank is located - is reported to be intact, the spokesman added.

Officers from the MCA are working to remove the fuel from the stricken vessel.