Baby formula manufacturers have confirmed there is a shortage of their products in Australian stores because of unprecedented demand from overseas.

Some supermarkets have now restricted the number customers can buy.

Contamination in baby formula products sold in China has led to product recalls in that country, and many Chinese buyers have turned to the Australian and New Zealand markets.

Although producers had stepped up their manufacturing to meet the demand in both the overseas and local markets, there would be a temporary lag as production caught up, the companies said.

A spokesman for Coles said it was working closely with suppliers to increase its stock.

“However, until the supply issue is fully resolved, sales quantities have been limited to four units per customer to ensure formula is available to all customers,” he said.

Woolworths has had an eight-tin limit for several years.

Consumers have been encouraged to buy online from the website of their preferred brand where possible.

Some people appear to be taking advantage of the temporary in-store shortages by selling formula for marked-up prices on eBay and other online shopping sites.

A spokeswoman for Danone Nutricia, maker of Aptamil toddler products, confirmed the range was available through its online stores.

“Over the last three months we have increased production of Aptamil Gold Plus Toddler by 50%, and Aptamil Profutura Toddler fourfold,” she said.

“Our New Zealand factory is now producing 24 hours a day through the week, and we have implemented a weekend shift. We have logistics teams working incremental shifts to ensure stock flows efficiently out of our facilities.

“Despite these measures, we are limited in the amount of raw ingredients we can access, and there is only so much that can be produced each day.”

An outcry over the shortage was renewed on Tuesday after a Victorian woman shared photos on social media of customers bulk-buying a trolley full of formula at a Woolworths store, in breach of the eight-tin limit.

The chief executive of the A2 Milk Company, Peter Nathan, said he was aware of customers in Australia bulk-buying A2 Platinum baby formula to send to their relatives in China. The company also ships its products to China.

“It is frustrating, as we would clearly love to be able to fulfil all of the demand for our products,” he said.

“However, there is a lag time in production, as we only use cows that only produce milk containing the A2 type of a protein, and we have only been producing the product for about two years so we’re still growing.”

In a statement posted to its website, Bellamy’s Organic baby formula said it had experienced unprecedented demand for its products throughout October.

“Although we have dramatically increased our supply over this period, this has been insufficient to keep pace and this, in turn, has meant that we have had to supply our supermarket and pharmacy customers with limited stocks that are quickly exhausted,” the statement said.

“Whilst it takes some time to ramp up supplies of organic formula, we have the situation in hand and expect stocks to improve from late November onwards. We appreciate how frustrating this is for mothers, but please bear with us a little longer.”

Bellamy’s confirmed its products were still available online.

“We will enforce our current policy of only supplying to Australian and New Zealand addresses and a limit of three tins per fortnight per customer,” the statement said.