Updated 4.50pm:
Assistant Commissioner for Road Policing Glenn Weir has made an impassioned plea to motorists after a horror weekend on Victorian roads.
This included the deaths of two males and two females who died in a crash near Hamilton on Saturday.
A fifth female teenager remains in a critical condition in the Alfred Hospital.
"This year we have seen a significant number of multiple fatality collisions," Mr Weir said.
"It's unacceptable and it cannot go on.
"Do something now before you too either suffer road trauma or - as we've seen some terrible examples over the weekend - you will know someone who does."
Mr Weir said it was believed the vehicle was travelling at high speeds and some passengers may not have been wearing seatbelts.
"The vehicle has obviously been travelling at extremely high speed," he said.
"We'll do a full forensic crash reconstruction to try and understand what has happened."

Mr Weir said it was hoped the 17-year-old passenger in hospital would recover and be able to help police with details of what led to the crash.
He said the victims were yet to be formally identified but it was believed there was a 30-year-old female and two male teenagers in the car.
Mr Weir said police across the state to raise awareness about the dangers of speeding and driving while distracted.
"Families have been ripped apart - a community has been ripped apart - it can't go on," Mr Weir said.
Police are reviewing CCTV from a waterfall close to the crash, where the vehicle was filmed at 1am before the vehicle was discovered about 9am.
"We have got a lot of CCTV at a waterfall nearby," Mr Weir said.
Updated 2pm: Premier Daniel Andrews has extended his sympathies to the families of the four people killed in the accident near Hamilton on Saturday.
"This will be an incredibly difficult time for those families, friends, people who loved those who have been caught up in this, and we send our best wishes during what will be an incredibly challenging time ... people should be assured there'll be a full investigation ... so that we could try and understand what's happened," he said.
Mr Andrews urged all Victorians to take care on the roads.
Updated 11am Sunday:
The Hamilton community is mourning the loss of four people in a crash at Bochara on Saturday, Southern Grampians mayor David Robertson told The Standard on Sunday.
"The whole community is in shock at the moment," Cr Robertson said.
"We will all probably start realising what's happened soon.
"Our hearts go out to the families."
Cr Robertson said the crash was "every parent's worst nightmare".
"I have children and grandchildren and you just always hope that something like this doesn't happen.
"Everybody in the community is going to be affected by this tragedy."
Cr Robertson said the community was rallying behind the families, with support being offered from a number of agencies.
He said it would be a very tough time for the Baimbridge College community.
"Our thoughts are with the school teachers and their school mates," Cr Robertson said.
He said there would be ripple affects to the whole community.
"There is a lot of support being offered in Hamilton to the family and friends," Cr Robertson said.
"Please reach out if you need to - we are here to help."
Sergeant Ryan Nelson, who was at the scene of the crime on Saturday, said the fifth occupant of the car was flown to the Alfred Hospital with upper body injuries.
"Hamilton's a very tight-knit community and there's five people involved in this .. it's going to hit the town very hard," Sergeant Nelson told Nine News.
"There's a lot of people out there who want answers and we want to give those people those answers but we just need the time to investigate."
The ages of the four deceased have not been released by police.
Updated 9am Sunday:
Two males and two females died after a crash near Hamilton on Saturday.
Victoria Police initially reported four females had died at the scene.
Major Collision Investigation Unit detectives remain at the scene of the fatal crash at Bochara.
The area has been cordoned off while police investigate the crash.
Anyone who witnessed the collision or anyone with dashcam footage is asked to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppersvic.com.au
Earlier
Four people have died and another critically injured when their car hit a tree near Hamilton on Saturday.
Police said investigators have been told the car - which was carrying five people - was travelling along Wannon-Nigretta Road about 9.30am when the driver lost control of the vehicle.
The car left the road and hit a tree at Bochara - about 10 minutes north west of Hamilton, police said.
Four females, who are all yet to be formally identified, died at the scene.
Another female has been taken to hospital with serious injuries.
An Ambulance Victoria spokesman said paramedics were called to the scene at 9.54am.
A teenage girl was flown to The Alfred in a critical condition with upper body injuries, he said.
Major Collision Investigation Unit detectives are investigating the circumstances surrounding the crash.
Emergency services are currently at the scene and the area has been cordoned off while police investigate the crash.
Anyone who witnessed the collision or anyone with dashcam footage is asked to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppersvic.com.au
So far this year 124 lives have been lost on Victorian roads compared to 96 at the same time last year.
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