The woman, who was 38 weeks pregnant, was one of two passengers in the car when it crashed yesterday.
Police said the driver of the car helped drag a woman and a male from the wreck moments before it caught fire.
Described by police as a "ride from hell", the car slammed into a tree and burst into flames near Waipukurau.
Emergency services responded to the one-car crash on Middleton Rd, about 8km southeast of the Central Hawke's Bay town, just after 2pm yesterday.
Waipukurau Police Senior Constable John Flack said initial investigations suggested the car, carrying three people, left the road on a corner while heading south, before "flying" across a ditch and hitting a large tree head-on.
"The car appears to then have spun around before it later caught fire."
He said the driver noticed his passengers, including the 20-year-old woman, were seriously injured in the accident and the car was moments from igniting.
"He's managed to pull his mate, who had a severely broken leg, from the front passenger's seat and out of the car as it would've been starting to catch fire.
"Dragging him away, and ignoring the obvious pain he would have been in himself, he's pulled him on to the bank and away from the flames and it appears he has also helped free the pregnant woman and get her on to the road before the ambulance arrived."
Police said late last night the mother had lost her baby as a result of the injuries suffered in the crash.
St John Hawke's Bay district operations manager Stephen Smith said when paramedics arrived their immediate concerns lay with the pregnant woman.
"She was in a serious condition with abdominal pain and taken by helicopter to Hawke's Bay Hospital.
"The other passenger had serious leg fractures, while he and the driver were also suffering from abdominal pain. "
Waipukurau Fire Station chief Gary Weaver said his crew arrived and doused the burning wreck.
" It is very lucky that no one was burnt or was trapped and had to be freed from the wreck.
"Looking at where the car is, coming off that corner, it would have been a ride from hell."
Mr Flack said all three in the car were Central Hawke's Bay residents.
He added the driver may yet face driving charges in relation to the crash. Police investigations were continuing.
Last night a Hawke's Bay Hospital spokeswoman said the woman was in a serious condition in the high dependency unit, while the other passenger and driver were in a stable condition.
- Sam Hurley, Hawke's Bay Today
