The bodies of two boys have been found hours after police issued an amber alert for the missing children in Townsville.

Key points: Police said the boys were seen swimming in the river

Police said the boys were seen swimming in the river Their mother said during the search she was "tired and empty" and missing her boys

Their mother said during the search she was "tired and empty" and missing her boys More than 100 people and a helicopter searched overnight

The brothers, aged 3 and 5, disappeared from a property on Brett Street in Cranbrook on the city's south about 5:30pm on Monday.

WARNING: Aboriginal and Torres Strait Islander readers are advised that the following story contains images of people who have died.

CCTV captured the boys walking along Brett Street towards Ross River, yesterday afternoon.

Their bodies were found in the Ross River near Cranbrook Park early Tuesday morning.

The boys' mother posted on Facebook during the search to say she was "tired and empty" and missing her boys "so, so much".

She thanked people searching for her sons and had earlier pleaded with others to look for them, and share their photos on Facebook.

Detective Senior Sergeant David Miles said the boys were found in the water within metres of each other.

"They were in a small cutaway area in the river, from recent flood events it's quite deep, and quite a deep bank, and there's some vegetation there," he said.

"We have a large expanse of water which is unfenced, it's got access to the entire Townsville community.

A CCTV still of the two boys walking towards Ross River. ( Supplied: Queensland Police Service )

"This is just a tragic set of circumstances where these young boys have ventured down to the river and obviously got caught up in the environment."

Detective Senior Sergeant Miles said a number of residents had reported seeing the boys on Monday afternoon.

"We have young boys who are very familiar with their surroundings. They, like other children, play in the community," he said.

"We have to look at all circumstances at this point before we make any determinations as to whether or not there's anything we should be concerned about.

"It could be as innocent as harmless play that's had tragic consequences."

Police are doorknocking residents in the area in the hopes of finding witnesses.

The boys went missing from their Townsville home. ( Supplied: Queensland Police Service )

More than 100 people and a helicopter were involved in a "methodical" overnight search of the area.

Townsville Aboriginal academic and activist Gracelyn Smallwood said the Indigenous community was in shock and overwhelmed by the support during the search.

"All children are precious. And our love and hearts go out to the families, the mums, grandparents and the community because Townsville's had such a tragedy with the floods and we're just coming to terms with so many of our people in town losing property, but nothing can take the place of this terrible loss of two little innocent children who regularly come and play in the park," she said.

Flowers at a makeshift memorial for the two boys on the banks of the Ross River. ( ABC News )

"Of course [the boys] are probably so used to swimming there and the recent floods have probably made the conditions very bad. I can't imagine the pain and suffering the parents are going through and we all send our love and prayers."

Townsville Mayor Jenny Hill said the loss of two young lives was a tragedy.

"Nothing can replace the loss of life, and nothing will replace these children in the arms of their family or in the hearts of their family."

Member for Townsville Scott Stewart said the deaths were heartbreaking for the community.

"My thoughts and prayers go out to the family of these kids; I can't imagine what they are going through — the anguish, the heartbreak," he said.

Mr Scott commended locals who spent the night searching for the boys.

"It's that Townsville strong spirit that we have … we band together, we look after one another, and this is where we stand strong together and this is where we rely on the community to get us through these tough times," he said.