A baby found dead in a stormwater drain is believed to have been about two weeks old.

The horrifying discovery of the infant was made in Alexander Heights in Perth’s north on Monday afternoon.

West Australian Premier Roger Cook said the baby was believed to have been about two weeks old.

Know the news with the 7NEWS app: Download today

He initially misspoke, saying the infant had been there about two weeks. It was later clarified he meant the infant was only about that old.

“The mother of that child must be incredibly distressed,” he told reporters on Tuesday.

It is understood tradies found the body while cleaning the drain on Monday, in what Cook described as a “horrifying scenario”.

“Those workers that discovered the child’s body were confronted with the most distressing of circumstances,” he said.

“My heart goes out to everyone involved in this horrible, horrible series of events.

“This goes to the heart of everyone’s sense of humanity, a small child whose life has passed under tragic circumstances.”

WA Police confirmed the investigation into the grim discovery remained ongoing.

Anyone with information has been urged to contact police.

If you need help in a crisis, call Lifeline on 13 11 14. For further information about depression contact beyondblue on 1300224636 or talk to your GP, local health professional or someone you trust.