Single-use plastic bags will be a thing of the past at the checkouts of Woolworths and Coles in the next 12 months.

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.