A man has died working on the controversial Corrib gas tunnel in Co Mayo.
Gardai and the Health and Safety Authority (HSA) launched separate investigations into the accident in Aughoose.
It is understood the employee sustained fatal head injuries while operating a tunnel-boring machine at the pipeline at about 9am.
He was pronounced dead at the scene, where his body remains.
A spokesperson for the HSA said investigators are on their way to the accident scene which has been sealed off.
Shell Ireland appointed BAM Civil and Wayss & Freytag, both of which are subsidiaries of the Royal BAM Group, as contractors for the 4.9km Corrib tunnel which will run under Sruwaddacon Bay i n north Mayo to the Bellanaboy Gas Processing Terminal.
In a statement the firms said the deceased was a German national who worked for Herrenknecht, a subcontractor.
"Operations were immediately suspended at the tunnelling site and a full coordinated investigation has been launched into the incident," it said.
"The joint venture is co-operating fully with the Garda and Health and Safety Authority investigations which are under way at site.
"The management and staff of Wayss & Freytag and BAM Civil express their sincere condolences to the family of the deceased, whose details will be released once all his next of kin have been informed."
The controversial Corrib gas field lies about 80 kilometres (50 miles) off the north-west coast of Ireland and th e onshore pipeline works is the final phase of the scheme to be completed.
The tunnel boring machine (TBM), which has an an internal diameter of 3.5m (11ft 5in), was imported last summer and is being used for the work. When the tunnel has been constructed and the TBM removed, the 20in gas pipeline will be installed in the tunnel.
The accident happened in the tunnel, 1.8km (1.1 miles) under the bay.