In a shock announcement on Friday afternoon, Woolworths revealed it would shortly begin phasing out the bags in supermarkets, Big W and BWS stores, with a total ban in place by June 30 next year.

The move was welcomed by environmental groups, which have long campaigned for a national plastic bag ban, and prompted calls for Woolworths' chief competitor to follow suit.

Less than two hours later, Coles announced it, too, would be phasing out single-use plastic bags over the next 12 months.

It is understood Woolworths was unaware Coles would be making an equivalent announcement on Friday.

The phase-out will bring stores for both supermarket giants in NSW, Victoria and Western Australia in line with those in other states and territories where plastic bag bans have been legislated.

South Australia, ACT, the Northern Territory and Tasmania have already implemented state-wide bans, while there are plans in place for Queensland to do the same next year.

"We currently give out more than 3.2 billion lightweight plastic bags a year and hence can play a significant role in reducing overall plastic bag usage," Woolworths Group chief executive Brad Banducci said.

"Our customers can also expect further commitments in reducing plastic use in all parts of our supply chain, especially in fruit and vegetables ... we feel this is an issue we need to take a stand on."

Woolworths' Dan Murphy's and Cellarmasters stores have already stopped handing out single-use plastic bags.

Instead of single-use plastic bags, the stores will now sell "a range of alternative shopping bag options [which] includes thicker reusable versions" at the checkout. Big W stores may provide reusable bags at no extra cost.

In a statement, Coles said the announcement followed several months of consultation with a number of non-government organisations and environmental groups.

"We've been working towards this announcement for some time now as part of our ongoing program to improve environmental outcomes throughout our business," Coles chief customer officer Simon McDowell said.

Coles will continue to provide a range of reusable bags at different prices.

Total Environment Centre director Jeff Angel, a major advocate of a plastic bag ban, said he was "a little surprised" by the Woolworths announcement on Friday.

"Woolworths has been one of the more oppositional stores [to a ban], so if they can announce such a good decision then clearly all of the previous objections are null and void," he said.

Upon hearing that Coles had announced its own ban, he said there were "now no obstacles for all states to announce a ban on the checkout bag at all stores when they meet on July 28".

"We welcome these announcements but would like to see them go the whole hog and ban plastic at the checkout entirely."

Australians use about 6 billion plastic bags every year, Clean Up Australia's managing director Terrie-Ann Johnson said.

"This will have a huge impact ... really, the only ones giving them out now at the supermarket level are Woolies and Coles."

Ms Johnson said supermarkets were most likely pre-empting an official ban on plastic bags in the remaining states and the decision is unlikely to cost them any money.

German supermarket chain Aldi, which opened in Australia in 2001, has never provided single-use plastic bags at the checkout and sells multi-use bags for 15 cents and fabric bags for 99 cents.

It is estimated that tens of millions of plastic bags end up in Australia's waste streams every year and are frequently ingested by wildlife.

More than half the turtles around the world and two-thirds of some bird species found on Australia's east cost have ingested plastics, according to CSIRO research.