The US space centre that was due to welcome a group of Victorian high school students has fully refunded the trip after a bus carrying 27 of the group crashed on its way to the airport.
Several students from Ballarat's Loreto College were injured when their bus crashed down an embankment on the Western Highway at Bacchus Marsh in the early hours of Wednesday after it was hit from behind by a truck.
The pupils from years nine to 11 were travelling to Melbourne Airport for a flight to visit the US Space and Rocket Centre's Space Camp.
The rocket centre's chief executive, Kimberly Robinson, told AAP the facility was distressed and saddened to hear of the terrible accident.
"Our thoughts and prayers are with these students and teachers and their families during this difficult time," she said.
The centre said all families had been provided full refunds and it would work with the school to rebook the trip when students were ready.
Loreto College principal Michelle Brodrick said the school would stay open on Thursday despite the national day of mourning for Queen Elizabeth II to allow students, families and carers to access counselling.
Police described the students' escape from the crashed vehicle as "miraculous".
"I think it was fairly harrowing for everyone involved - how anyone wasn't more seriously injured is incredible," Victoria Police acting Superintendent Jason Templar told reporters on Wednesday.
Speed limits at the time of crash had been reduced following a collision the previous night.
Three teenage girls at the Royal Children's Hospital are in a stable condition.
A woman in her 40s and a man in his 50s remain in Royal Melbourne Hospital in a stable condition.
Kangaroo Transport Industries chief executive Steve Buck said the 60-year-old driver was a sub-contractor "who has been safely driving road trains for more than 30 years" and needed surgery after being trapped in the cab.
The other 25 students on the bus and four adults were taken to hospital for observation after the incident, police said.
Grampians Health's Ballarat Base Hospital treated 16 patients from the crash, with 13 of them discharged on Wednesday afternoon.
Premier Daniel Andrews offered support to the school after speaking to the principal on Wednesday.
The Melbourne-bound lanes of the Western Freeway between Ballan and Bacchus Marsh have since re-opened, but the eastbound Bacchus Marsh Road exit ramp remains closed.
Major collision unit detectives are investigating the exact circumstances of the crash.
