The nation's biggest supermarket chains are one step closer to ditching all single-use plastic shopping bags, with Woolworths phasing them out on Wednesday and Coles to follow in just over a week's time.

"We really believe in a greener future," Adrian Cullen, head of sustainability for Woolworths, told Fairfax Media. "This is going to make a significant impact to the environment."

Sylvia Bui, a nursing student, leaving a Woolworths store in central Sydney with her reusable shopping bags on Wednesday. Credit:Janie Barrett

Woolworths and its partner outlets such as Big W dispense about 3.2 billion plastic bags a year. Shoppers have the option of buying thicker bags using 80 per cent recycled plastic for 15 cents, or "Bag for Good' cloth bags for 99 cents.

"I think it's quite cheap," said Sylvia Bui, a nursing student who bought two of the bags at the retailer's outlet near the Sydney Town Hall.