MELBOURNE, Aug 10 - The pair were killed while leaving a Cranbourne East car park on Wednesday night when they were hit by a silver Commodore, which police believe may have been speeding.

They died at the scene.

Lighthouse Christian College principal Jacob Mathews says he's been asking authorities to lower the speed limit near the school from 100km/h for two years.

"We have asked for an 80km/h zone here, there are 80km/h zones both south and north of us," he told 3AW on Thursday.

He says the girl was at school for parent-teacher interviews, where she received glowing praise from her teachers.

"All the teachers were saying how she had improved so much and then (she goes) out the door and a car hits her."

The school is now supporting its tight-knit community and the victims' family.

"We are all family here. We are a small community. We are all Christians. We all go to church together," Mathews said.

"Many of the staff are crying away ... she will be sadly missed by all students as well as the teachers."

School excursions and NAPLAN testing set for Thursday have been cancelled.

Crash investigators are examining whether speed or alcohol were factors in the collision, but have been told the Commodore was seen overtaking a number of vehicles on the highway before the crash.

"We believe the Holden Commodore has left a licensed premises in Cranbourne prior to the crash," Detective Senior Sergeant Gerard Clanchy told Seven News.

The driver, aged in his 20s, was taken to hospital suffering serious injuries.

Mathews says the current speed limit did not reflect the changing nature of the area, which has become increasingly residential.

"Hopefully, we will see something come out of this situation," he said.