A Melbourne bus crash has left multiple children with 'traumatic' injuries. Here's what we know.

A Melbourne school community remains in shock today following a serious school bus crash that has left multiple students with injuries.

On Tuesday afternoon at 3:40pm, a bus carrying 45 students from Exford Primary School collided with a truck. The school bus was hit from behind, and the impact caused the bus to roll onto its side.

Multiple children were trapped inside the bus before witnesses and emergency workers pulled them from the wreckage and they were transported to hospital.

Watch: Royal Children's Hospital CEO Bernadette McDonald provides an update on how the children impacted by the school bus crash are going. Post continues below.

Victoria Police Superintendent Michael Cruse said when emergency services arrived, they were met with a "horrific scene" at Eynesbury, 44km west of the Melbourne city centre.

"The bus driver, despite being injured, I understand that he helped some of the children out of the bus," Superintendent Cruse said.

"Then we had passers-by who have heroically stopped immediately, assisting the children who could be removed from the bus. It was chaotic and it would have been really confronting for those passers-by, so I think a special mention to those people."

He also confirmed that some of the people who responded to the accident were from the school community.

In total, there are 10 children who sustained injuries.

Out of the 10, there are seven who remain in hospital – aged five to 11 – and one student remains in intensive care.

Emergency services and police have said the most difficult consequence from the crash is that one child has undergone a complete amputation, and several others are undergoing partial amputations.

As for the two adults involved in the crash, the male bus driver sustained minor injuries while the male truck driver was also injured and said to be shaken, as per AAP.

Victoria Police Superintendent Michael Cruse and Exford Primary School Principal Lisa Campo speak to media. Image: AAP.

The children impacted and their injuries.

Seven children are still in a serious condition, with four undergoing surgery overnight, one in intensive care and another two going into theatre on Wednesday.

Three patients are receiving spinal support.

A Code Brown – an emergency response for hospitals anticipating mass casualties – was declared at Melbourne's Royal Children's Hospital after the crash and ran until 8pm.

Specialist doctors were called in to perform emergency surgeries after the children were admitted.

Royal Children's Hospital CEO Bernadette McDonald said many of the children will need to undergo multiple surgeries and long-term rehabilitation therapy is likely to be needed.

"The children have suffered multiple and traumatic injuries including partial and complete amputations of arms, multiple crushed limb injuries, severe lacerations to head and body, head injuries, glass shard injuries and three patients are currently receiving spinal support," she said.

McDonald said that many of the parents weren't reunited with their kids until the early hours of the morning.

"We have some very traumatised families and children in our hospital at the moment and we are working extremely hard to provide that trauma support and care that they will need."

Counsellors will also be going to the Exford Primary School to help students process the tragedy.

The school's principal says it's been a harrowing time.

Exford Primary School Principal Lisa Campo described the moment she received the call about the crash.

"We were expecting a fender-bender [a minor collision], not anything more than that," she said. 

"Our staff just instinctively wrapped their arms around the kids and provided love and support and comfort in a really, really difficult situation. I know we're not supposed to hug kids, but that's what they needed us to do and we hugged."

Speaking at the media conference, she also thanked the school's community and wider Australian public for their "love and support".

Charges now laid.

Police are now investigating whether a truck driver who was charged over the bus crash that left multiple children seriously injured was distracted in the lead-up to the Melbourne collision.

The 49-year-old man was charged with four counts of dangerous driving causing serious injury on Wednesday.

Superintendent Cruse said, "inattention is something that we are actively looking at as part of the investigation".

Premier Daniel Andrews said he had been in contact with the school, and Prime Minister Anthony Albanese said his "heart goes out" to all impacted.

Superintendent Cruse finished his statement saying, "Some of the injuries are truly life-changing – and this incident was avoidable, as are so many of the incidents that police and emergency services attend to."

More to come.

With AAP.

Feature Image: AAP.