Bystanders rushed in to help after a crash between a truck and van that killed seven, including an infant, on Sunday morning south of Picton.
St John operations support manager for Tasman District Murray Neal told 1News the bystanders did an "amazing job".
"We had a number of bystanders on scene who had some good medical training and were able to assist us and the patients quite early on," he said.
"Bystanders are often the first on the scene and do an amazing job for something they aren’t trained to do."
Nelson Bays area commander Inspector Paul Borrell said two people have been taken to Wellington Hospital after the crash. One is in a critical condition and the other person is in a serious condition.
He confirmed that the child who died was under the age of one.
Borrell said family members of the child may have been in the van at the time of the crash, but that details were still being confirmed.
The driver of the truck has minor injuries and is in Nelson Hospital.
Borrell also said early indications were that the van, which was carrying nine people, crossed the centre line to collide head-on with a refrigerated goods truck.
But it was too early to know the exact cause of the crash yet and a "variety of things that may have happened", Borrell said.
He said the van was travelling towards Picton while the truck was travelling south from the town.
Investigations were continuing.
He said the crash happened around 7.30am at Mount Pleasant on SH1.
"It's just absolutely tragic how, in a blink of an eye, seven lives are lost."