The Transport Management Centre says the Oxley Highway between Walcha and Long Flat could be closed until late Thursday or Friday.
The closure was implemented last weekend due to flooding.
Spokeswoman, Nicquie Sinclair, says the Centre is continuing to liaise with the local council.
She says as soon as the road is passable an announcement will be made.
"The Oxley Highway is still closed between Long Flat and Walcha and that's due to flooding and it is expected to remain this way until at least tomorrow afternoon," she said.
"So, we are advising motorists they can use the New England Highway or Grafton Road and Waterfall Way instead, but if you do need to travel these alternative routes they will add considerable time to journeys."
The Transport Management Centre re-iterates its warning to all motorists that it is not safe to attempt to drive through a flood-affected road when closure signs are in place.
© ABC 2013
08:03 EST An amazing video shows an Oklahoma tornado survivor being reunited with her dog when it is found in the rubble of her flattened house as she is being interviewed on US television.