Seven people have died, including an infant, and three people are injured following a horror crash between a van and a truck near Picton on Sunday morning, police have confirmed.
Police said a head-on crash north of Koromiko involving a van and a refrigerated goods truck happened at about 7:30am.
"Along with the deceased, one person has critical injuries and one has serious injuries," Tasman District Commander Inspector Paul Borrell said.
Insp Borrell added the people injured in the crash were flown to Wellington Hospital.
He said the driver of the truck received minor injuries.
"The seven deceased and the two flown to Wellington were travelling in the van. One of the deceased is a child," Insp Borrell said.
In a media conference on Sunday afternoon, Insp Borrell said the scene was "absolute carnage" and confirmed the child killed in the crash was an infant under the age of one.
Police said the van was heading north towards Picton, while the truck was heading south.
The initial assessment is that the van - with nine occupants inside - crossed the centre line.
"At the moment we are still establishing what has happened, but it would appear the van has crossed the centre line," he said.
"There is a variety of things that may of happened but I can't comment on any of those things until we've had a thorough investigation completed."
Insp Borrell urged drivers to slow down while driving.
"Our absolute condolences go out to the families. It's absolutely tragic how in a blink of an eye seven lives are lost. So our emergency services are devastated we are attending events like this," Insp Borrell said.
"Again a reminder for everyone single one of us, in a blink of an eye, seven lives are gone. We don't yet know the exact cause of the crash but research tells us that most injuries and fatal accidents, the contributors are speed, distractions, lack of restraints and sometimes impairment."
Marlborough Area Commander Inspector Simon Feltham said it was "a horrific thing" for emergency services to deal with and added for one of their staff it was just their third day on the job.
Police said the highway south of Picton remains closed while emergency services attend the scene and is likely to remain closed for most of the day but hope to have it re-open this afternoon.
"Marlborough disaster victim identification (DVI) staff are at the crash scene, as are staff from the serious crash unit," Insp Borrell said.
Police said their focus was on supporting the victim's families.
"Any death on our roads is a tragedy, let alone multiple fatalities in one crash," Insp Borrell said.
"A crash of this scale has a huge impact on both the community where it happens, that of the deceased's family and community, and on emergency services who attend.
"Police's focus remains on ensuring victims are supported and that the circumstances of the crash are fully investigated."
St John said in a statement it responded to the crash with three ambulances, one manager, one first response unit and two helicopters.
Crews treated three people for varying types of injuries, St John said.
"We assessed and treated three patients; one with critical injuries and one with serious injuries - both flown to Wellington hospital - and one with minor injuries transported to Wairau Hospital via road."
Waka Kotahi said State Highway 1 south of the Lindens Rd intersection is expected to be closed all day and advised motorists to delay their journeys - as there are no detours available.
A post on the Interislander ferry's Facebook page said it would delay the 11am sailing until 11:30am because of the crash.
"There has been a serious accident and the road to Picton is currently closed. If you are booked on the 11am Aratere sailing to Wellington we can delay the ferry until 11:30," Interislander said.
"If the road remains closed we will transfer your booking to the Kaitaki which departs at 2:15pm this afternoon. Please drive carefully."
