St John District operations manager Stephen Smith said paramedics arrived to find the boy bleeding on the road with lacerations to his face, body and arms.
Hawke's Bay road policing manager Sergeant Clint Adamson said the car was headed towards Diaz Drive and struck the boy in a dimly lit area, with no witnesses to the crash. He said a gathering crowd of neighbours may have frightened the driver into fleeing the scene.
"It's possible the driver was not at fault as the boy was coming down the driveway on his bike, however he did stop and pull into Peary Crescent and stop - people had obviously heard thenoise and come out of their homes which may have scared him off.
"It was right in between two street lights, so the timing couldn't have been worse, the lighting is pretty poor but not uncommon for a street like this ... it appears to be a low speed accident but if the driver was going any faster it could have been much worse."
Mr Adamson said police wanted to ask the driver why he didn't come back to the scene.
"When a driver hits something it is their responsibility to stop and ascertain if someone has been injured."
He said some neighbours claimed the car sounded as if it had suffered some damage from the crash as it drove away.
When Hawke's Bay Today went to print last night the child, who was accompanied by his father, was still being assessed at Hawke's Bay Hospital and was in a serious condition.
Police last night continued to hunt for the driver and the car, described as a black two-door Honda.
Earlier, emergency services responded to a two car crash on the Hawke's Bay expressway which left an 18-year-old male and a female passenger, believed to be in her early 20s, with neck and spinal injuries.
Senior Constable Ian Cheyne said the 18-year-old driver was pulling out of the Links Rd intersection, heading towards Hastings, when a car travelling north collided with his car at full speed.
St John District operations manager Stephen Smith said both the male and female had suffered moderate to severe injuries.
"The male's side of the car took the brunt of the impact - they had to cut him out and be a little more careful because ambulance staff were worried about his neck and back."
Mr Cheyne said the 18-year-old had failed to give way at the intersection and confirmed the driver of the other vehicle was unharmed.
"It's simply a case of taking your time and taking a second look because at 100km/h you often don't get a second chance."
A Hawke's Bay Hospital spokeswoman last night said the 18-year-old male was in a stable condition.
Also earlier in the morning, a 4-year-old boy had a lucky escape when the car his father was driving ploughed into the back of a parked truck in Flaxmere.
The driver of the car was affected by sun strike while driving down Livingstone Rd, in Flaxmere, at approximately 8.25am, said Senior Constable Bryan Farquharson.
He said the boy, who was in the front seat, and a 6-year-old in the back were both properly restrained and were not injured.
"The back of the truck went right through the passenger side window.
"It stopped just short of the child, he wasn't seriously injured but was taken to hospital. It was really good too see that everyone was strapped in properly."
Mr Farquharson said the father was "traumatised" by the accident and would not be charged.
"I'll just be warning him, it's a well known corner for sunstrike."
Both children were taken to hospital for observation but were discharged yesterday afternoon.
