A man and a woman were both critically ill in hospital on Friday night following two separate motorcycle accidents.
In Co Tyrone, a 20-year-old woman was badly injured when her machine crashed on the Clanabogan Road near Omagh early on Friday morning.
No other vehicles are thought to have been involved in the incident.
Police came across the scene around 1.35am and tasked an ambulance.
The woman was taken to a local hospital for treatment but was later transferred to the Royal Victoria Hospital in Belfast due to the severity of her injuries.
On Friday night a Belfast Health and Social Care Trust spokeswoman described the motorcyclist as being in a “critical” condition.
Part of the Clanabogan Road was closed for several hours but was reopened later on Friday morning.
Police have appealed for anyone who may have seen a black Honda motorcycle in the area in the early hours to contact Omagh police station on the non-emergency number 101.
There have been a number of serious collisions on the Clanabogan Road in recent years - including a fatal accident in March 2012.
On that occasion, a man in his 40s died when the car he was driving was involved in a late afternoon collision with a bus.
The Clanabogan Road, between Omagh and Dromore, was also closed for several hours last week due to a road accident, although no one was reported to have been seriously injured.
On June 26 last year, two cars collided close to the junction with the Brookmount Road just before 9am, while in January 2015, a 52-year-man was seriously injured as a result of a two-car collision at the Clanabogan Road’s junction with the Dromore Road in the early hours of the morning. Two other casualties were also treated in hospital.
In north Belfast, a 21-year-old man was seriously injured when his green Peugeot motorcycle was involved in a collision with a silver Mercedes car in Donegall Park Avenue on Thursday evening.
The incident took place around 9.45pm and police are appealing for any witnesses to come forward. He was taken to hospital for treatment to his injuries and last night a Belfast Trust spokeswoman confirmed he remained in a critical condition also.
PSNI Inspector McBride said: “I would appeal to anyone who may have seen the motorbike or car in the area to contact Tennent Street police station on the non emergency number 101.”