A young man remains in a critical condition in Christchurch Hospital after being involved in a head-on collision yesterday morning, 1km east of the Arthur's Pass township.
Darfield Police Station senior constable Dave Watkins said today the driver of one of the vehicles, a man in his early 20s, suffered life-threatening injuries.
He was flown to Christchurch Hospital in the Westpac Rescue helicopter.
The crash happened about 10am. Police said one of the vehicles was travelling towards Arthur's Pass and the other to Christchurch when they collided head-on.
Mr Watkins said the seriously injured man was heading towards Arthur's Pass and the Christchurch couple in their 50s were travelling in the opposite direction.
Police believe one of the vehicles crossed the centre line.
"The couple escaped, miraculously, after their Land Rover Discovery left the road and rolled down a 30m bank."
Mr Watkins said both walked away with minor injuries.
State Highway 73 between Otira and the Waimakariri River Valley Rd was closed just after 10.30am and did not reopen until after 3pm.
Motorists heading from the West Coast to Christchurch were stopped at Otira because Arthur's Pass was packed with people returning to Christchurch after Saturday's Around Brunner cycle race.
Police are not releasing the name of the critically injured man until next-of-kin have been advised.