Agriculture Minister David Littleproud says the coronavirus pandemic poses no risk to the nation’s food security.

The Nationals deputy leader said Australia produced enough food for 75 million people – three times its population.

“There is no risk of us having any issues around food security,” Mr Littleproud told ABC News on Thursday.

He said the only pressure on supply chains was coming from the ceaseless panic buying.

“They need to take a deep breath, have a cold shower and understand that if they shop normally, then the shelves will be stocked normally,” he said.

Mr Littleproud is the latest politician to try to re-assure shoppers, as supermarket shelves continue to be stripped of basic products and outbursts of violence increase.

On Tuesday, NSW Police arrested a 63-year-old man after a fracas over flour in a Lismore supermarket.

They said the man rammed his trolley into two women in their 70s after realising his local Coles had run out of flour.

A 45-year-old female store attendant was pinned against a shelf and punched in the face during the uproar. The store manager and a security guard were also allegedly attacked.

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It is the latest in a series of violent incidents in supermarkets across Australia since the coronavirus outbreak began to escalate – including a stabbing at Rosebud in Victoria and a man being tasered after a violent argument in Tamworth in NSW.

On Thursday, NSW Police said they would increase patrols to try to quell the hysteria.

“Police are making a concerted effort to ensure the security of shoppers and retail staff across the state amid concerns of panic buying due to COVID-19,” NSW police deputy commissioner Jeff Loy said.

Supermarkets have restricted online deliveries, put on dedicated shopping hours for the elderly and disabled and imposed limits on a host of pantry staples. But to no avail.

Woolworths chief executive Brad Banducci said the retail giant had “been asked to feed 50 million Australians and not 24.5 million Australians” in the past week – “and that is the big issue”.

“It’s unequivocally true that it’s a demand surge,” Mr Banducci told ABC’s 7.30 on Wednesday night.

“If everyone just bought what they needed, we would rapidly see a full shop again in ourselves and in all of our competitors.”

Coles chief operating officer Matt Swindells said shops were geared up to put products on the shelf as quickly as possible. The company has employed more than 5000 extra casual staff.

“There is lots and lots of stock in the system,” he told Nine’s Today Show on Thursday.

“The suppliers are producing more than ever, faster than ever and  … we’re moving record volumes into our stores.”

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Business Council of Australia chief executive Jennifer Westacott said supermarket staff had been abused by people looking to strip shelves of essential items or frustrated because items weren’t available.

“It’s unfair and it’s unnecessary. There’s no supply problem here. There’s a selfishness problem,” she told ABC radio.

Prime Minister Scott Morrison issued his own blunt message to people hoarding food on Wednesday.

“Stop it. It’s not sensible, it’s not helpful and I’ve got to say it’s been one of the most disappointing things I’ve seen in Australian behaviour in response to this crisis,” he said.

“That is not who we are as a people.”

He was backed up by Victorian Premier Daniel Andrews and WA Premier Mark McGowan – Mr McGowan said the state’s police had increased patrols to put a stop to “jerks, drongos and bloody idiots”.

On Thursday, the South Australian government said it would allow the state’s supermarkets to extend their opening hours to try to alleviate the panic shopping.

The temporary trading times – 24 hours on weekdays and extended hours on weekends – will begin on March 21 and run until April 19.

SA Treasurer Rob Lucas said the move provided much-needed flexibility for consumers and retailers.

“While we don’t expect all supermarkets to take up the option of 24-hour trading, extended hours will also assist with supply of grocery stock,” Mr Lucas said.

“We expect this exemption will also support local jobs, with the potential for more shifts for those employees who’d like to work additional hours over the next few weeks.”

-with AAP