A woman has been charged with attempted murder for allegedly trying to drown her son, as the search for a missing 5-year-old boy is called off for the day.

The 27-year-old will appear in Deniliquin Bail Court tomorrow after being extradited from Victoria to New South Wales.

She previously appeared in Bendigo Magistrates Court sobbing uncontrollably as details of her alleged offences were read out. The court heard how she allegedly told witnesses the night before the incident that she "had to drown my babies".

Her nine-year-old son is in a Melbourne hospital in a serious condition after undergoing surgery following a dog bite.

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Police have called off the search for a missing 5-year-old boy due to bad light and it will be resumed first thing in the morning.

Police allege the woman took her children to the Murray River, near Moama, and told her eldest son, 9, to get into water and tried to drown him.

Detective Sergeant Trent Swinton told the court the younger son, 5, was screaming during the incident. The older boy managed to struggle free when the woman turned to the younger boy. He was last seen drifting facedown in the water.

After escaping from his mum, the older boy was "savagely mauled" by a dog.

Screams were heard by people on the riverbank but they did not witness the incident, the court was told.

Detective Sergeant Swinton said the woman had told police of her intention to kill both children, and also allegedly told witnesses the night before that she "had to drown my babies".

The woman did not apply for bail and was transferred into the custody of NSW Police. She will appear in the Deniliquin Local Court tomorrow.

Lawyer Dale Brooks, who is representing the grandmother of the boys, told news.com.au the 27-year-old was a long-time ice addict and well-known to local authorities.

Brooks said the woman took the grandmother's car on Wednesday night, snatched the two young boys and took off with a couple of her buddies.

Brooks said government agencies had "culpability" for what happened to the two boys on Thursday.

"The mother in this instance has been a really troubled individual, she's been a long term ice addict," Brooks said.

Despite the grandmother taking out an apprehended violence order against the woman last year, authorities still expected them to live together.

He said the grandmother had complained to government agencies numerous times about the woman's behaviour and tried to get her removed from her home. However, she kept being told there was no where for the woman to go.

In the last couple of days, one officer even raised concerns about the woman's mental health but still nothing was done.

"If she presented in a way that was worrying, why weren't steps taken to have her taken into institutional care?" Brooks said.

Shortly after, Brooks said the woman took the grandmother's car, snatched the two young boys and left with a couple of her buddies.

"They deserved greater protection," Brooks said of the family.

"I think they (the agencies) have some culpability in this case."

Brooks said the grandmother was "heartbroken" about what had happened.

Marine rescue NSW search the Murray River for a missing boy in Moama, NSW. Photo / News Corp
Marine rescue NSW search the Murray River for a missing boy in Moama, NSW. Photo / News Corp

Deniliquin commander Superintendent Paul Condon told reporters today the case was "just terrible" and that "it will rock the community of Australia".

"It is a terrible story. It is a sad story. It's a tragic story. Not only for the community, the police but especially the family. It's just terrible," he said.

There was speculation a pit bull acted as a hero dog that stopped the mother from allegedly drowning her son, but Supt Condon said it was unclear what role it played in last night's events.

"It is very unclear at this stage as to what happened at the riverbank. The dog has been involved. The dog has bitten the 27-year-old mother and the nine-year-old. The actual circumstances are unknown," Supt Condon said.

The owner of the dog, Buddy, did not want to be named but told The Herald Sun the dog was trying to save the boy from drowning.

"The dog is four years old and it's never attacked one person, has grown up with kids, and it's always been around kinds playing," she said.

She said her partner and his friend were on the property at the time and helped save the child when they found him in the river.

The pair "rushed the little boy to the hospital".

In an earlier statement, Supt Condon said: "Contrary to rumours, the dog was not set on the child. This has been an extremely traumatic scene for all the first responders involved and welfare support is being offered."

He said the dog belonged to a local family.

Search continues for missing 5-year-old

Meanwhile, searchers continue to comb the Murray River in Moama, on the border of NSW and Victoria, today looking for the missing 5-year-old.

When asked what the chances were the five-year-old would be found alive, Supt Condon said: "There is every chance. We all live in hope".

However, he said searchers had not recovered any material from the riverbank, despite reports a small T-shirt was found.

Police were alerted by neighbours when the boy's brother, 9, was found with serious dog bite injuries about 7pm.

Supt Condon said neighbours found the boy and told police they had taken him to the hospital. Authorities realised the boy's mother and brother were missing and began a search.

Later the mother, 27, presented herself to police at Echuca in Victoria about 10pm and was taken to Echuca Hospital to get treatment for a dog bite. She was released and then went to the police station for questioning.

Boy is 'distressed'

Police spoke to the 9-year-old briefly last night.

"He required some surgery on the dog bites at this stage and of course, he is distressed. He is a nine-year-old boy," Supt Condon said.

About 25 to 30 searchers are combing the river for the boy's missing 5-year-old brother from NSW and Victoria Police, SES and the rural bushfire service. Victorian Police divers have also been searching the river.

Further murder charges could be laid against the woman depending on the results of the search.

"It is devastating," the spokesman said. "My police are devastated. The community is."

- Additional reporting: AAP