Two fuel tanks have been "breached" on an oil rig carrying 280 tonnes of diesel that ran aground on the Western Isles.
The Maritime and Coastguard Agency said it is "unclear at this time" how much oil from the tanks has been released to the environment.
The drilling rig Transocean Winner was blown ashore in severe weather conditions on the western side of the Isle of Lewis early on Monday after the semi-submersible rig detached from its tug during towing and severe weather prevented the line being reconnected.
No-one was on board when it grounded at Dalmore beach near Carloway.
People are being urged to stay away from the beach and a temporary 300-metre exclusion zone has been set up.
Salvage teams were winched on board the rig by helicopter on Tuesday to assess the damage but have been unable to return due to bad weather in the area.
The diesel was being stored in a number of tanks on the rig, two of which seem to have been damaged.
Environmental groups had raised concerns about the incident but the pollution risk was believed to be low.
An MCA spokeswoman said: "The rig remains in the original position and was reported to be carrying 280 metric tonnes of diesel oil on board in total split between a number of separate tanks.
"During the inspection the salvors discovered that two of the fuel tanks appear to have been breached, however it is unclear at this time how much oil from those tanks has been released to the environment.
"Weather conditions have made it impossible for the team to continue the assessment today.
"Additional salvors and technical experts from Transocean, and also equipment, continues to arrive to the incident area to support the operation.
"A temporary exclusion zone of 300 metres to keep boats away remains in force.
"The tug Union Bear remains in the vicinity along with the ETV Herakles to support the operation.
"Hugh Shaw, the Secretary of State's representative for maritime and salvage, continues to monitor the operations and is maintaining touch with all the key stakeholders, including Transocean, Smit Salvage, the Scottish Environment Group and Western Isles Council."