'Unimaginable sorrow': Mother and children drown on family outing in Sydney

A baby boy has lost his mother and two siblings after the trio drowned in a waterway in Sydney's south-west yesterday.

Hoai Nguyen, 32, and her two children, Mitchell, seven, and Hazel, five, had been at Shearer Park at Lansvale in Fairfield yesterday when they were spotted struggling in the Georges River about 10.15am.

Hoai was pulled to shore shortly afterwards, but despite the efforts of a number of bystanders and emergency services, couldn't be saved.

READ MORE: Warm welcome for King and Queen as royal couple attend church service

Police and volunteers from the State Emergency Service launched a large search and rescue operation for the two children.

Divers found their bodies in the water at about 2pm, metres from a jetty.

A family friend has set up an online fundraiser to raise money to support the children's father, Hoai's husband, and their one-year-old brother during the "time of unimaginable sorrow".

9News understands the father was at work yesterday and heard the news when he returned home to find police at his door.

READ MORE: Boy, 5, seriously injured after rock thrown through train window

"A beloved mother and her two young children tragically drowned... leaving behind a profound void in our hearts and a father and baby who is only 1 years old," the fundraiser reads.

Today floral tributes, incense and offerings were left on the jetty, just metres away from where the tragedy unfolded.

The Vietnamese community is rallying around the family as close friends share tributes online.

"I hope you and your 2 little ones will rest in peace in the golden stream," an online tribute reads.

"2 days ago I (just) talked to you… Absolutely and deeply shocked to hear this news."

NSW Police acting superintendent Luke Scott yesterday described the tragedy as "beyond words".

The investigation into how the mother and her children ended up in the water is ongoing.