"We have technical consultations with the unions regarding safety and environmental impacts of the actions. No units are down at this point," she said in a statement.

"We see no opening at this point to further continue with the formal negotiations," she added.

The Dutch FNV union said the strike action over pay by workers would bring gradually reduce production at the plant to 65 percent of capacity.

"They won't be able to get to the 65 percent unless they do shut it down but we are not at that point yet," the Shell spokeswoman said.