A boat has exploded on the Hawkesbury River north of Sydney, leaving four people fighting for life with critical burns.
Eight people suffered burns and smoke inhalation in the explosion at Brooklyn near Danger Island on Sunday afternoon.
NSW Ambulance confirmed four of those on board were critically injured in the Easter Sunday incident that drew at least a dozen emergency crews.
They were taken to Royal North Shore Hospital under police escort.
Another two patients were transferred to Westmead Hospital in a serious condition, while the remaining two others were treated at the scene.
"NSW Ambulance along with other emergency services established a triage area to assess all of our patients," NSW Ambulance inspector David Morris said in a statement on Sunday evening.
"Once the area was established, patients were reassessed by NSW Ambulance medical teams.
"NSW Police provided assistance in escorting these patients to various hospitals with medical teams awaiting their arrival."
Fire and Rescue NSW said firefighters were tasked with driving ambulances to allow paramedics to treat patients in transit because of the seriousness of their injuries.
The vessel has sunk in shallow water with a slow fuel leak, with hazardous materials experts called in to contain it.
The cause of the fire is under investigation.