Mum Lauren Petersen watched in horror as closing train doors left her two daughters, aged 5 and 3, stranded on the platform at Paremata, near Porirua.

A Porirua mum was separated from two of her young children when a train's doors closed before she could follow them on to the platform.

Lauren Petersen, of Whitby, frantically pushed the button to open the doors, but nothing happened, and the train started to pull out of Paremata station on Monday evening.

Five-year-old Chelsea and 3-year-old Zara were left standing alone on the platform as Petersen and 1-year-old Georgia headed for the next stop at Porirua.

MONIQUE FORD/STUFF Lauren Petersen, with Chelsea, 5, Georgia, 1, and Zara, 3. She and Georgia were stuck on the train while Chelsea and Zara were stranded on the platform at Paremata station on Monday.

She pleaded with a TransDev staffer to stop the train, but says he told her "I'm sorry", before racing to the front of the train.

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Petersen took the children for a school holiday outing to Paraparaumu on Monday. When the 5.20pm service from Waikanae got back to Paremata, she told Chelsea and Zara to get off first.

MONIQUE FORD/STUFF "I couldn't believe there was no-one standing with these two kids in peak hour when they've just seen them crying, chasing a train," Petersen says.

"I pressed the button to open the doors and said, 'Hop off, girls', and they took a big step.

"They stepped out and then the doors started to shut on the front of my pram.

"I tried to press the button to open the door but it didn't do anything, and the next thing the train starts to move."

In panic, she looked for an emergency stop button but couldn't find one.

She begged the train staffer to stop the train.

"The first thing I said was, 'You need to stop the train'. I said, 'How the f... did you let this happen?', then I obviously broke into tears and started shaking."

Once the train got to Porirua, the staffer offered to find out when the next Paremata-bound train was due, but Petersen called police instead, who were able to check on Chelsea and Zara through the station's CCTV cameras.

A police spokeswoman confirmed a call was received about 6pm.

"Traffic operations centre cameras were able to be utilised to sight the children on the platform, who it appeared were being looked after by a member of the public," the spokeswoman said.

"A police vehicle was dispatched to the station but was stood down as the mother arrived first."

Meanwhile, a stranger who saw the incident and got off at Porirua gave Petersen a ride back to Paremata.

TransDev spokeswoman Emily Liddell said it appeared the train was incorrectly given the all-clear to leave the station.

"There were other passengers disembarking at the station. I believe the staff member thought the children were with their parents, and they gave the right of way to say passengers were clear of the door."

The error would be followed up by the company, as was standard procedure with any incident, Liddell said.

However, she believed the correct on-board procedure was followed, as the staff member immediately "escalated" the situation, alerting TransDev's service control centre, which monitored CCTV cameras.

There were emergency buttons on-board trains for passengers to alert staff members to an incident, but not to stop the train, she said.

Petersen described the incident as "probably one of the worst experiences of my life".