President Nicolas Maduro rolled out supermarket loyalty cards in his latest effort to stop fascist-inspired coup attempts against Venezuela's government.

Using a tactic eerily reminiscent of the destabilisation that preceded the Chilean coup in 1973, extreme rightwingers have been disrupting the country's basic supplies.

Registration for the new cards - which keep track of families' purchases to stop them hoarding food and then selling it for hugely inflated prices on the black market - began at more than 100 government-run supermarkets .

Working-class shoppers, who are often forced to queue for hours for food, welcomed the news.

"The rich people have things all hoarded away and they pull the strings," said Juan Rodriguez, who waited two hours to enter the government-run Abastos Bicentenario supermarket in Caracas on Monday and then another three hours to check out.

Checkout workers took down customers' phone numbers to ensure they could not return for a week and banned children from making purchases to stop parents using their kids for hoarding.

Mr Rodriguez supported the measures: "People who go shopping every day hurt us all," he said, drawing approving nods from fellow shoppers.

But government opponents claimed that the move was simply rationing by another name.

The new system will see shoppers register with their fingerprints and will flag up people with suspicious purchasing patterns - such as buying the same goods every day.

Food Minister Felix Osorio said the cards would be voluntary, but have incentives like discounts and entry into raffles for homes and cars.

Meanwhile, the opposition has continued to wage its economic war against the socialist government.

Merida residents narrowly avoided having their main water supply contaminated after 100 litres of diesel were dumped into a water plant.

An engineer at the plant spotted the contamination, which would have unleashed a public health disaster, before flowed into the main pipes.