The New England Highway has been closed in both directions following a two vehicle car accident at 11.10am near Haggartys Lane in Whittingham.
Emergency services are in attendance with a Westpac helicopter (arriving at 12:18am) on the scene.
Authorities urge motorists to allow approximately 25 minutes of additional travel time.
As of 2.30pm, northbound traffic is crawling at a snail's pace while Range Road is only open to residents until further notice.
Alternative routes recommended include the Golden Hwy (Mitchell Line of Rd) and Putty Rd to travel between Whittingham and Singleton.
Light vehicles already in the area are being diverted into Range Rd.
UPDATE FROM NSW POLICE 12:35PM:
Emergency services are at the scene of a serious two-vehicle crash on the New England Highway.
Just before 11.15am today (Friday 12 July 2019), emergency services were called to the New England Highway at Whittingham, 500m north of Range Road, after reports a car and a 4WD had crashed head-on.
The female driver of the car and a child passenger are in a critical condition and are being treated at the scene.
Two other children are also being treated for non-life-threatening injuries.
The male driver and sole occupant of the 4WD has been taken to John Hunter Hospital with non-life-threatening injuries.
Officers from Hunter Valley Police District have established a crime scene as they investigate the circumstances surrounding the crash.
The road is expected to be closed for some time, with local traffic diversions in place.
Heavy vehicles are advised to look at alternative routes.
No further information is available at this time.
Anyone with information about this incident is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au. Information is treated in strict confidence. The public is reminded not to report crime via NSW Police social media pages.
UPDATE FROM WESTPAC RESCUE HELICOPTER SERVICE 1:26PM:
The Westpac Rescue Helicopter is transporting a six year old boy from Whittingham to John Hunter Hospital suffering multiple injuries sustained in a MVA on the New England Highway.
The patient is in a serious condition.
No further details.