A distressed mother is pleading for answers after her son became trapped in the doors of a school bus before being dragged down the road in Melbourne.

The 12-year-old was on his way to school in Wheelers Hill in the city's south-east on March 16 when his bag appeared to become caught in the automatic bus doors.

Phone camera footage, released today by the boy's mother, shows the schoolboy being carried down the road by the public bus, as he lifted his knees to avoid being scraped along the bitumen.

His mother Grace shared the confronting footage on Instagram and said another school mum saw her son hanging off the bus and honked to warn the driver.

It is understood the boy was dragged for about 350 metres down the street before the bus driver noticed.

"It still gives me anxiety every time I see the footage, it's just horrible," Grace told Today.

"When the bus took off he knew that he couldn't keep running at its side so he just had to lift his legs off the ground.

"And honestly, if he was a taller student, or a weaker student, there is no way he would be able to hang on to the side of a moving bus, at that speed, for that distance."

Grace earlier told 3AW that her son, who had just started year seven this year, was mostly uninjured.

He was left with some bruising on his shoulder from the strap of his schoolbag.

"We're very, very thankful that he is physically unhurt," she said.

"I don't know how it happened.

"He could have died... he could have clipped the side [of the] cars."

Grace said her son is now "traumatised" and does not like to catch the bus to school alone.

"[He] is still seeing a psychologist, but he can't travel on the bus alone anymore and he gets panic attacks when he sees a bus on the road," she told Today.

Grace called for safety improvements to ensure a similar incident does not occur.

"The bus door only has one sensor in the middle of the door and Nathaniel was caught under that sensor, so it didn't set off any alarms for the driver," she said.

"However, the door wasn't fully closed, his arm was caught in it, you would think there would be another sfaety feature on the bus to alert the driver of that."

"Ventura [the bus operator] are not being accountable, the responses I have received from them so far have been very dismissive and just very disappointing.

"We need our children to be safe. This should not have happened to [my son] or anybody else, it's just horrible."

Nine.com.au has contacted Ventura Bus Lines and Victoria's Department of Transport for comment.

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