Health workers blocking roads near Argentina's large Vaca Muerta shale oil and gas deposit on Monday rejected a government wage offer and vowed to continue a three-week protest that is threatening a national fuel shortage.

Workers in the region are demanding higher wages amid a fierce second wave of the country's COVID-19 epidemic. They include hospital orderlies, maids, nurses and doctors who have erected some 25 roadblocks around the town of Anelo, in Neuquén province, about 1,000 km south-west of Buenos Aires.

Argentine state-run YPF (YPFD.BA) produces nearly 13% of the country's oil output at Vaca Muerta and there are fears that local fuel shortages could soon extend nationwide.

Other companies operating in the area include Shell (RDSa.L), Vista Oil (VIST.BA) and Pan American Energy.

Local media have reported long lines at gas stations, while fuel-hauling trucks are being prevented from entering production areas. Vaca Muerta workers have been arriving at the site by helicopter, the TN news channel said.

Argentina wants to boost production at Vaca Muerta in order to reduce its energy imports as the government seeks export dollars to protect central bank reserves.

Protesters said they had rejected a wage offer by the regional government after assemblies of workers and said a deal was not in sight.

Irma, a public hospital receptionist, told local television the government had offered a 53% salary increase paid in installments until April 2022, but workers wanted an immediate 40% cash increase given high inflation and risks from COVID-19.

"We know we're causing problems by not letting fuel and goods trucks through, but someone has to listen to us," said Anahi, a nurse blocking a route near the town of Rincón de los Sauces.

Some analysts have warned that with the start of the southern hemisphere winter, gas could also soon start to become scarce.

Argentina's Public Prosecutor has weighed in, since roadblocks are illegal, setting itself up as a mediator in the dispute.