An investigation has been launched after a grandfather mistakenly took home the wrong child from a daycare centre in Sydney, Australia.

The man arrived to collect his grandchild from First Steps Learning Academy in the southern suburb of Bangor, on Monday afternoon.

But he accidentally took home a different child, who was asleep in a dark room.

The mistake only became clear when the mother of the child arrived at the centre to find that her one-year-old was not there, the Sydney Morning Herald reported.

"I can't explain the feeling," she told the newspaper.

"They couldn't tell me [the man's] name, they couldn't tell me who he was, they couldn't tell me who he was meant to pick up. They couldn't tell me what he looked like, apart from that he was wearing shorts and he was an older gentleman," the mother, who asked not to be named, explained.

As part of safety protocols, childcare centres do not allow children to be collected by anyone else except recognized parents, guardians or carers.

But she also said the grandfather is not to blame.

"We are not angry with him. We are not upset at him - we blame the daycare."

The grandfather's wife told the Sydney Morning Herald that her husband was "devastated" and had "owned the mistake".

"When he realized, he raced that child back so fast," she said.

First Steps told the BBC that the worker involved in the incident had been stood down.

"We sincerely apologize to the families directly involved in this deeply upsetting and isolated incident," nursery director Trisha Hastie said.

She added that it had never happened before at any of First Steps' nurseries, which had since strengthened procedures to "ensure this never happens again".

An investigation is under way into the "deeply concerning and serious incident", the New South Wales Early Childhood Education and Care Regulatory Authority said.

The incident comes at a time of heightened awareness surrounding safety at Australia's childcare centres, and last month, new legislative changes were announced aimed at improving safety standards in the sector. (BBC)