Bert, Ernie, Big Bird and Cookie Monster have traded Sesame Street for the bush, getting acquainted with a kaleidoscopic menagerie of kangaroos, birds, grubs, mantises and reef fish on one of Australia's biggest and most visible canvases.

The unmissable, 15 metre-wide Worra Munga! Ernie and Bert Dreamtime voice will greet more than one million visitors passing through the foyer of Sydney's Museum of Contemporary Art and along the teeming Circular Quay outside.

The gallery commissioned celebrated Walmajarri artist John Prince Siddon to update their yearly foyer mural, which he dedicated to children enduring conflict.

The space has featured murals depicting scheming demons, colliding histories, and fleeing refugees in previous years.

"I'm trying to get a message to a leader really," Siddon told AAP.

"Nobody's listening ... the government won't listen, so I do the painting, I'll explain, and I'll try and get a message to them."

It's certainly a hard message to ignore.

Siddon has spared none of his palette, interlacing ancient concepts with thoroughly modern characters, marrying symbols and allusions from all over Australia to gesture at a dazzlingly diverse but harmonious world.

But viewers' eyes first magnetise to the huge weeping ancestor in the centre of the mural, which Siddon said conveyed a yearning for one's own place.

"I see many old people around the nursing home, and I can't read their mind but they're probably thinking about moving back to their country," he said.

Then, a few metres to the right, over a dozen colours and shapes, childhood TV staples Bert and Ernie smile at visitors from behind criss-crossing green vines.

Siddon himself hails from Western Australia's Great Sandy Desert, a part of Australia about as far from Sydney as it's possible to get.

"I like to mix everything," he said.

Aficionados and passers-by will have plenty of time to catch sight of the mural, as the gallery will keep it on the foyer wall for two years rather than the usual 12 months.

"We have just been so blown away," exhibit co-curator Tim Riley-Walsh told AAP.

"As this was coming together, we thought this is something that needs more time, it needs more opportunity for the public to come in and experience it."