A design fault in the plans for a new sea lock at IJmuiden is costing construction companies BAM and Volker Wessels a further €100m, the NRC said on Wednesday.

The two building giants, which have already taken a €38m loss on the project, are working together on what will be the biggest sea lock system in the world, the paper said.

BAM said on Wednesday that the losses had forced it to revise down the group’s 2017 forecast – a cost over-run described as ‘very disappointing’ by chief executive Rob van Wingerden.

‘For BAM, this will lead to an estimated additional project loss of around €55m in the fourth quarter of 2017,’ the company said in a statement. ‘As a consequence, BAM expects an adjusted result before tax for the full year 2017 which will be substantially lower compared to 2016.’

The new lock, 70 metres wide, 500 metres long and 18 metres deep, will allow bigger freight and cruise ships to reach Amsterdam.

It was due to be completed in 2019 but that deadline has since been extended. When commissioned in 2015, the budget for the project was put at €600m.