Train services through Lincolnshire were severely disrupted when a railway worker was hit by a train.
He was on the track at Newark Northgate Station when the incident happened on Wednesday morning.
The man was airlifted to Nottingham Queen's Medical Centre with head injuries.
A Network Rail spokesman said: "Our thoughts are with our staff member and his colleagues and family. The safety of our team is of the utmost importance and a full investigation of the circumstances will be carried out."
A British Transport Police spokesman said: "Officers are working to establish the circumstances surrounding this incident, which is being treated as non suspicious."