The Seagate plant in Limavady, Co Derry, closed this morning with the loss of more than 900 jobs.
The US-owned company announced the closure almost a year ago, saying the operation had become uncompetitive.
Seagate Technologies opened in Limavady 11 years ago, manufacturing computer hard drives and other information storage products.
It has been a major employer in the northwest, along with its associated plant in Derry city, which is not affected.
Some of the 900 workers made redundant last year came from across the border in Co Donegal.
A skeleton staff was kept on to run down the facility and much of the company's work will now be carried out in Malaysia.
Yesterday, Northern Ireland First Minister Peter Robinson told business leaders that Northern Ireland could not shelter itself from the global marketplace.
Despite today's closure, he said there were still many positive factors which would help to sustain some growth in the economy over the next year.
