The semi-submersible rig detached from its tug during towing
Two fuel tanks have been "breached" on an oil rig carrying 280 tonnes of diesel that ran aground on the Western Isles, or Outer Hebrides, in Britain.
The UK Maritime and Coastguard Agency said it is "unclear at this time" how much oil from the tanks has leaked to the environment.
The drilling rig Transocean Winner was blown ashore in severe weather on the western side of the Isle of Lewis early on Monday.
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 they 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.
"The tug Union Bear remains in the vicinity along with the ETV Herakles to support the operation."
A damage assessment team has been sent to carry out a series of initial inspections.