Experts fear the salvage operation to remove a stricken oil rig from the Isle of Lewis could take weeks due to the enormity of the task ahead.

The rig was carrying 300,000 litres of diesel when it ran aground and salvage experts are now trying to ascertain the severity of damage that has been sustained.

The Transocean Winner is believed to have leaked more than 50,000 litres of diesel since it was blown ashore in severe weather conditions on the western side of Lewis.

The semi-submersible rig detached from its tug the Alp Forward during towing from Norway to Malta and the weather prevented the line being reconnected.

Now, salvage teams are working to board the rig in order to conduct a thorough inspection before deciding what action to take.

A team of eight salvors were unable to be winched down on Saturday afternoon and now other options, including boarding from the sea using a rope access team, are being explored.

The team did, however, manage to climb partly up the installation and will return tomorrow to find a safe route onto the main deck, weather permitting.

Experts are hopeful that the rig can be refloated as soon as Thursday during a period of high tide, but have warned that the operation could stretch into weeks rather than days.

A spokesperson for the Maritime and Coastguard Agency said: "We're still very much at the information gathering stage.

"We've lost a lot of time this week, just the fact that we've been unable to check the tanks.

"We're still trying to understand the damage itself so we're certainly looking at what, in my opinion, would be weeks as opposed to days.

"I'm not saying that we won't make it, but I think that there is a lot of work that would need to be done between now and then."

Hugh Shaw, the secretary of state's representative for maritime salvage and intervention, said: 'We are aware of how much interest there is still about this rig locally and we completely understand.

"We've been working alongside local emergency services and other organisations to make sure that everyone's well informed about the next steps and we will continue to share information with others for that reason."