Sydneysiders have been warned to “keep their ‘littlies’ close” after at least 10 children have ended up travelling solo on the city’s new driverless trains when the automated doors closed abruptly, leaving distraught parents stranded on the platform.

Children and their parents have been separated at least 10 times in the first three months of the Metro’s operation – and the rail union fears there are more to come.

Last week, a two-year-old boy in his pram was left to ride without his mother for more than 10 minutes after they were separated while boarding at Macquarie University.

Transport Minister Andrew Constance said he was “concerned” about the incidents and wanted parents to take more care when catching the driverless trains.

“I remind everyone that the doors on Metro trains are automatic and people should move onboard quickly, and parents and carers should keep their littlies close – hold their hands and pay attention,” the minister said on Thursday.

Mr Constance said he was “naturally concerned” about children being separated from parents or carers, but noted there’d been more than 5.3 million passenger journeys on the Metro since it opened in late May.

Metro staff assisted the children and parents in all 10 incidents and they were quickly reunited, a spokeswoman said.

The automated doors of Metro carriages stay open for about 30 seconds at each platform.

When the doors begin to close, lights flash, there’s a beeping sound and an announcement is made.

A spokeswoman for the minister said the announcement was louder than elsewhere on the NSW trains network.

@SydneyMetro just watching the loads at chatswood and 20 seconds to 30 seconds is not enough time to load when there is a large crowd waiting to board.
Needs to be at least 60 sec esp when there is prams

— Jackryan (@Jackrya29719409) August 28, 2019

Each Metro train has 18 entrances across six carriages. It is understood there are staff on every platform but they do not monitor each door.

Rail, Tram and Bus Union NSW secretary Alex Claassens said the incidents were to be expected, given there were too few staff to ensure passenger safety.

“This is what happens when you run a transport system without adequate staff on board – the safety of commuters goes out the window,” he said.

“The sad truth is, these incidents will continue.”

The $7.3 billion Sydney Metro has been plagued with problems since it began operating, with more than 30 significant disruptions, including train doors malfunctioning, urgent mechanical repairs and track work.

Last Friday, much of the Sydney rail network was brought to a standstill after power had to be disconnected for urgent repairs to a train at Town Hall Station.

-AAP