A 62-year-old man died and four others were injured after a two-car collision near Strabane on Wednesday.
The crash happened on the Melmount Road between Sion Mills and Victoria Bridge around 10.50am.
The Fire Service sent four appliances to the scene and used cutting equipment to release five casualties.
A PSNI spokesman said the collision involved a black coloured Suzuki Vitara jeep and a blue coloured Toyota Avensis.
The deceased was a passenger in one of the vehicles.
Two men – one aged in his 20s and one aged in his 40s – and two women – one aged in her 20s and one aged in her 50s – were last night being treated in Altnagelvin Hospital in Londonderry.
The health trust did not reveal their condition.
SDLP West Tyrone MLA, Joe Byrne and Strabane councillor Patsy Kelly last night expressed their sadness at news of the crash.
Mr Byrne said: “This is tragic news. My heart goes out to the families of those involved and I offer my deepest sympathy.”
Councillor Kelly added that it was “heartbreaking to hear another life has been lost on this stretch of road”.
She went on to extend her deepest sympathy to the families of the victim and those injured.
Meanwhile, the funeral for the man killed in a suspected hit-and-run collision in the Tullychurry Road area of Leggs, Belleek, Co Fermanagh, on Sunday will be held on Thursday.
Pat John McCafferty, 49, who was originally from Pettigo in Co Donegal, will be buried after 11am Requiem Mass in Saint Mary’s Church in Pettigo.
A PSNI spokesman said they are continuing to investigate the circumstances surrounding his death.
He said: “The blue Ford Focus believed to have been involved in the incident has been recovered and police are continuing to liaise with our colleagues in An Garda Siochana in relation to this investigation.”
The spokesman said a 40-year-old man was arrested by An Garda Siochana on Sunday and he was released pending a report to the DPP in the Republic.
“The PSNI intend to pursue a prosecution in relation to the death through the courts in Northern Ireland,” he added.
He appealed for anyone with information about the 2.50am incident to contact the PSNI in Enniskillen.