Twice a year for the past 13 years, a group called Keep Australia Beautiful has dispatched teams of "litter counters" to beaches, shops, roads and other sites across the country to survey the nation's litter.

They are trained to analyse the garbage and confirm that, say, bits of broken glass are counted as one bottle, or to distinguish between a piece of glass and clear plastic.

The result is an annual national litter index - an extraordinarily detailed account of the bits of rubbish strewn across 983 separate sites covering 1.5 million sq m.

As the Australian authorities and other countries around the world consider whether to ban plastic bags, this survey has proven useful in demonstrating a perhaps unsurprising result: Places with such bans end up with less rubbish.

According to the most recent report by Keep Australia Beautiful released on Jan 24, the four places in Australia with bans - South Australia, the Northern Territory, the Australian Capital Territory (ACT) and Tasmania - all recorded "overall lower levels of litter counts of lightweight plastic bags".

"It is evident... that the national litter index does 'detect' the change in policy settings, particularly evident in Tasmania and ACT, where lightweight plastic bag litter fell significantly and almost immediately after the bans came into effect," the report said.

The soaring amount of discarded plastics poses a growing environmental threat and has led to increasing efforts around the world to ban plastic bags.

Plastic shopping bags represent only a small amount of total litter, but pose a serious threat to marine wildlife and birds as they are not biodegradable. Studies have shown that lightweight plastic bags are blown away easily into waterways, are hard to recycle and are mistaken for food by some wildlife, especially in oceans as they resemble jellyfish. About three-quarters of coastal rubbish in Australia is plastic, including bags.

This has prompted a fresh push for bans in Australia, where an estimated six billion single-use bags are used each year, including some 50 million that end up in the environment.

The states of Western Australia and Queensland are introducing bans on lightweight, single-use plastic bags from July 1.

A public survey in Western Australia in November found that more than 90 per cent of people were concerned about the environmental impact of plastic and 84 per cent supported a state-wide ban on plastic bags, with 7 per cent opposed and 9 per cent uncommitted.

The state of Victoria is also set to introduce a ban this year.

This has left New South Wales (NSW), the largest state, as Australia's only state or territory without a ban or a proposed ban.

Meanwhile, major supermarkets and retailers - including Woolworths, Coles, Harris Farm and IGA - have voluntarily announced that they will ban single-use bags across Australia. Some provide bags but charge 15 Australian cents [$AUS](15.6 Singapore cents) per bag.

NSW Premier Gladys Berejiklian said the moves by retailers meant that a legislated ban was unnecessary, a position that has been heavily criticised.

An editorial in The Sydney Morning Herald said the state's decision to be the only state without a ban was a "mystery".

"On average, we use a plastic bag for 12 minutes. Only around 10 per cent are recycled in Australia, and they are made from fossil fuels," it said. "If we need an emblem of thoughtless consumerism, the single-use plastic bag is it."

Some experts say the push to ban plastic bags should be followed by a broader effort to reduce plastics, particularly in consumer packaging, such as for fruit and vegetables.

Still, there are growing concerns that the plastic bag bans are prompting people to use thicker bags, which they later discard.

The ACT is reviewing its ban amid concerns that outlawing thin bags has prompted stores to give shoppers thicker bags.

The territory's Climate Change Minister, Mr Shane Rattenbury, last week suggested extending the ban to thicker bags and allowing stores to dispense only those that are biodegradable.

"Many retailers and customers have not changed their behaviour around the use of plastic bags, and perversely may instead be using thicker plastic bags for single uses," he said in a letter ordering the review.

Despite the inaction of governments, some smaller communities across Australia have voluntarily opted to go bag-free.

In 2003, the tiny coastal town of Coles Bay in Tasmania became the first in Australia - and one of the first places in the world - to ban plastic bags.

Mr Jim Kearney, a local baker, said some 350,000 bags were being kept out of the town each year.

"The people in the town feel better about living in the town," he told ABC News in 2005.

"They feel like we're making a real effort to protect this wonderful, pristine little jewel that we've got here in Coles Bay."