Image copyright Getty Images Image caption More than 8 million tonnes of plastic ends up in the world's oceans each year

Tempers flared in Australia over the weekend as retailers implemented a ban on single-use plastic bags.

One customer reportedly grabbed a shop assistant by the throat, while another called staff "money-grabbing scum".

The ban on single-use bags is part of a national push to reduce waste. Retailers in four of six Australian states now face fines for using them.

More than 60 countries including the UK have now introduced bans or levies on single-use bags, according to the UN.

The UN environment agency estimates that up to 5 trillion single-use bags are consumed worldwide each year.

Australian chain Woolworths introduced a ban on the bags on 20 June, ahead of the 1 July deadline, offering reusable bags for 15 cents (£0.08; $0.11) instead.

But customer "bag rage" pushed the chain to reverse the policy and offer the reusable bags for free until 8 July.

"They just want a little extra help from us to get through the transition," said Claire Peters, Woolworths managing director, in a statement.

Another chain, Coles, said it would open every checkout lane on Sunday to reduce queue lengths and put on extra staff to explain the change to customers.

Video caption Five ways to break up with plastic

"We are taking a proactive step," a Coles spokesperson said.

A retail staff union urged customers to treat staff members with respect.

"While we understand that some customers may be frustrated by this change, there is absolutely no excuse for abusive or violent behaviour towards retail staff," said Gerard Dwyer, national secretary of the Shop, Distributive and Allied Employees' Association.

The union surveyed 132 of its members and said 57 reported suffering abuse over the ban.

How is so much plastic getting into the oceans ?

More than 8 million tonnes of plastic ends up in the world's oceans each year, according to the UN, which has called for single-use bags to be eliminated completely by 2022.

The main way that plastic gets into the seas is via the world's major rivers. Research suggests that 95% of plastic is transported in this way . Eight of these rivers are found in Asia.

Video caption Plastic pollution is killing animals in the Arctic

Most of the plastic comes from China, but Indonesia, the Philippines and Vietnam also rank among major polluters.

Consumer behaviour in developed countries including the UK, Europe and the US is also a major factor in pushing plastic into the world's waters.

According to figures, US citizens produce around 120kg (264lb) of plastic waste per person every year . The UK produces around 76kg (167lb) of waste while in Sweden, it's around 18kg (40lb).

What's the rest of the world doing?

Last December, 193 countries committed to a UN plan to stop plastic waste entering the oceans . But the commitment is not legally binding and doesn't have a timetable, and different countries have adopted different schemes.

Around 40 have banned single-use plastic bags, with charges or outright prohibitions in place in China, Bangladesh. and about 15 African countries.

Other nations, including the UK, are moving to ban plastic straws and cotton buds.