Preceding a press conference at the Sturt Street college this afternoon, principal Michelle Brodrick issued the statement to the Ballarat and school communities that have rallied in support following the horrifying early morning crash.

"This is an extremely difficult and upsetting time for the Loreto College community, " Ms Brodrick said in the statement.

"The College has today been in close communication with the families of students and staff involved and will continue to offer all support we can to the impacted and injured students and staff.

"Some students have been discharged from hospital into the care of their parents. A number of staff and students remain in hospital for treatment for varying levels of injury.

"The advice we have received at this stage is that all are recovering."

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It has also said the College would be open on Thursday for students, staff and families to be together, specifically to pray for the recovery of those injured in the accident.

Loreto will also offer counselling support to all members of the College community.

"On behalf of the College community, I would like to thank the first responders and medical personnel who are caring for our students and staff today, " Ms Brodrick.

"I also thank the many members of the community here in Ballarat and beyond who have reached out to offer their support.

UPDATED 11am: Dozens of schoolgirls and their teachers have had the trip of a lifetime to NASA in the USA turned into a nightmare after their bus rolled on the Western Freeway.

Loreto College Ballarat confirmed the students were on their way to Melbourne airport for the trip to the United States when the crash occurred early Wednesday morning near the Condons Lane exit.

Police earlier reported that multiple students sustained injuries in the crash, including one taken by air ambulance to Melbourne with serious injuries.

The truck driver also sustained serious injuries.

A spokesperson said all the parents of the students had been contacted early on Wednesday morning and those not taken to hospital had returned to Ballarat.

Grampians Health confirmed a Code Brown remains in place at Ballarat Base Hospital in response to the bus crash.

Ambulance Victoria has transported a number of students to the Ballarat Base Hospital, with others being transferred to Melbourne, Sunshine, and Footscray.

"Grampians Health can confirm that one Loreto staff member and 15 students were transferred to the Ballarat Base Hospital for treatment and observation following the accident, and all are in a stable condition," the hospital said.

"We can confirm that all students in our care have been reunited with their families, and some have been discharged home."

Police have local detours in place through Pentland Hills and Bacchus Marsh, although there are significant delays and motorists are encouraged to avoid the area.

The College issued a statement saying they were very appreciative of the quick and professional response of the Emergency Services personnel at the scene.

"Whilst our caring Loreto community will have deep concern for the injured, we will only be able to provide information of a general nature about the condition of students and staff in hospital. We thank for you for your understanding," it said.

"Our caring Loreto community has deep concern for the injured and their families and we ask for their privacy to be respected. We thank for you for your understanding."

The Premier Daniel Andrews also offered his support for the victims of the crash and the school community.

"My thoughts go out to the students, teachers and drivers affected, and the whole Ballarat community, " Mr Andrews said in social media post.

"I've spoken with Loreto College's Principal Michelle Brodrick and we'll give the school community all the support they need."

Things remained quiet at the Sturt Street college which is currently on term three holidays but some staff were attending the campus.

A police vehicle remains parked at the school.

Loreto College conducts its annual 'space camp' as an opportunity for its best students to learn first hand the wonders and achievements of space travel.

However many students have been denied the opportunity in recent years due to travel lockdowns brought about by the pandemic.

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READ THE FULL STATEMENT FROM AMBULANCE VICTORIA BELOW

Ambulance Victoria paramedics responded to a bus and truck collision in Pentland Hills at 3.20am this morning.

Paramedics assessed more than 30 people on scene for traumatic injuries, and transported them to hospital in various conditions.

Paramedics treated:

EARLIER: Police are investigating a collision between a truck and school bus in Bacchus Marsh early this morning that has seriously injured one teenager and could have affected dozens more.

The collision occurred about 3.15am on the Western Freeway, near the Condons Lane intersection, the first major intersection for Bacchus Marsh heading toward Melbourne.

The collision caused the bus to roll down an embankment, and one teenage girl was airlifted to hospital with serious injuries.

The male truck driver was taken to hospital by road with serious injuries.

The bus contained 27 female students, four adults and the bus driver - all will be taken to hospital for observation.

Ambulance Victoria has detailed some of those hurt in the collision.

A teenage girl with lower body injuries was also taken by road to the Royal Children's Hospital in a serious but stable condition and a man in his 50s with minor injuries who was taken by road to the Alfred Hospital in a stable condition, Ambulance Victoria reported.

"A woman in her 40s with upper body injuries who taken by road to the Royal Melbourne Hospital in a serious but stable condition and a man in his 50s who was treated for lower body injuries and taken by road to the Royal Melbourne Hospital in a serious but stable condition," the statement read.

It also listed a teenage girl with upper body injuries who was taken by road to the Royal Melbourne Hospital in a stable condition and a woman in her 40s with upper body injuries who was taken by road to Sunshine Hospital in a stable condition.

Two teenage girls with minor injuries were taken by road to Sunshine Hospital in a stable condition and a teenage girl with minor injuries who was taken by road to Western Hospital Footscray in a stable condition.

Details also include a teenage girl with back pain who was taken to Ballarat Base Hospital in a stable condition with a teenage girl with upper body injuries who was taken to Ballarat Base Hospital in a stable condition.

A further 11 people were taken by road to Ballarat Base Hospital, all in a stable condition.

The Melbourne-bound lanes of the Western Freeway are expected to remain closed for several hours and motorists are urged to take an alternative route.

Police have asked concerned parents seeking information regarding their children are asked not to attend the scene and to instead phone Ballarat Police Station on 5336 6000.

Police are investigating the circumstances surrounding the collision and urge any witnesses or anyone with dashcam footage to phone Crime Stoppers on 1800 333 000 or submit confidential report at crimestoppersvic.com.au

More to come.

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