Ninety oil workers have been evacuated from a North Sea rig as engineers fight to control a huge build up of pressure in a well which critics say has the potential to blow-up the platform and cause a major environmental problem.

The Norwegian company Statoil has been pumping cement into an offshore well on the Gullfaks field in an operation similar to the one being attempted today by BP in the Gulf of Mexico.

The equivalent of around 70,000 barrels of oil a day of production from the Gullfaks C, Tordis and Gimle platforms has been shut down and more than 90 staff evacuated from the area, which lies in Norwegian waters.

The country's industry regulator said it was the third well control incident on Gullfaks in the past six months.

Jake Molloy, offshore organiser of the RMT union in Aberdeen, said the case also highlighted the continuing dangers of oil extraction off Britain's coast. He added: "The huge gas bubble under the Gullfaks has the potential to threaten the platform."

However, Statoil said today that the well was being brought under control. "We had a build-up in pressure and the barriers (through the blowout preventer) worked as they should. We are now pumping cement into the well and the pressure is starting to fall," said Kai Neilsen, a spokesman for the oil group in London.

Nelson said the previous incidents on Gullfaks had not been serious but Inger Anda, a spokeswoman for Norway's Petroleum Safety Authority (PSA), said a well "kick", reported in December, was serious. A further incident on 30 April this year – also a gas kick caused by high pressure – was brought under control quickly.

Anda said the authority was having daily meetings with Statoil until the latest problem was resolved.

Gullfaks C started production in 1990. It is one of three large concrete-legged platforms comprising the huge Gullfaks development and stands in water 217 metres deep – much shallower than BP's Deepwater well in the Gulf. The unit taps oil from the Tordis field as well as taking in supplies from the Gimle and Skinfaks satellite fields.

The Bellona green campaign group said it was concerned about lax regulation in the North Sea. It described the Statoil field emergency as "very critical" and highlighted continued risks of offshore oil and gas exploration in the wake of BP's well blowout and environmental disaster off America.

"They have a situation in which there is uncontrolled pressure from the well, one of the barriers is gone and one barrier is left," said Frederic Hauge, head of Bellona, one of the leading environmental groups in Norway.

"Uncontrolled pressure is very serious and has the capability of being a large accident," he said, adding that in the first quarter of 2010, eight incidents took place in the Norwegian oil industry that could have had huge consequences. "That is very serious. Regulatory work in Norway may look nice from outside, but we have a lot of security issues in the Norwegian industry."