Greenpeace has sent a ship to the Elgin platform to take samples of the air and water.
The Koningin Juliana sailed from Germany to the North Sea around 150 miles east of Aberdeen.
The vessel will be spending around 24 hours gathering data from the scene.
Christian Bussau, chief scientist and ocean expert of the environmental campaign group, said: “We’ve sent it to the site as part of a preliminary assessment and bearing witness expedition.
“It has reached the Elgin gas platform and has started taking samples of air and water. The trip will last four days, with around one day spent at the site, before the ship heads back to Germany.
“The Greenpeace team has a sophisticated gas detection camera which may reveal more about the gas leak – although the conditions and site restriction may make this difficult.
“Greenpeace will adhere to all safety restrictions and does will not enter any exclusion zones.”
Mr Bussau added: “We are here because oil companies often withhold information on accidents. “We’re collecting first-hand information of the environmental damage. After more than a week of publishing the accident, there is still no information how long Total will need to close the gas leak.
“The exploitation of oil and gas will always cause accidents.”