The magnitude 6 earthquake that hit northern Italy at the weekend, killing seven people and toppling historic churches, castles and clock towers, has also taken a huge toll on the country's culinary culture.

Parmesan cheese producers near the quake's epicentre in flat farmland north of Bologna said 300,000 massive wheels of the cheese that were ageing on tall shelves in warehouses crashed to the ground.

"All the shelving toppled over like huge dominoes and only 20 to 30% of my wheels survived unscathed," said Ivano Chezzi, the manager of one facility where 90,000 wheels were aging.

After ageing for 12 to 24 months, three million 40kg parmesan wheels worth almost €2bn (£1.6bn) are sold each year from the region. Two-thirds of the output stays in Italy, and the rest – about 40,000 tonnes – is exported.

"The wheels that fell represent 10% of annual production," said a spokesman for the Parmigiano-Reggiano Cheese Consortium. Half of them might now be lost, he added, costing the business €80m, including the cost of repairing storage warehouses.

The wheels, which measure 40cm across, are stacked 22 wheels high on shelves standing up to 10m. Staff at the 10 storage sites hit by Sunday's quake were urgently picking through toppled shelves and smashed cheeses, looking for undamaged wheels and seeking spare storage with the correct temperature and humidity where they can continue to age.

One producer said it would take 20 days to fish out all the wheels. "If the cheeses have broken open they may go mouldy," said Leo Bertozzi, the director of the consortium. Wheels that have suffered minor damage may be sold at a discount for industrial use or grating, he added. "Seeing all those wheels everywhere really hit me in the stomach," he said.

To be considered genuine parmesan, the cheese must be aged in the area, and producers are now seeking an exception to the rule as they rebuild their warehouses. The wheels, which sell for up to €420 when fully matured for 24 months, are considered so valuable that a local bank offers to hold them as collateral on loans for producers. The loss of the wheels does not necessarily mean parmesan's price will rise, said Chezzi, due to a recent increase in production.

Producers of Grana Padano, a cheese similar to parmesan that is also grated on pasta dishes, reportedly lost up to 130,000 wheels during the earthquake. In a region known for the production of prosciutto ham, one farm lost more than 100 pigs when buildings collapsed.

Amid heavy rain and falling temperatures on Tuesday, about 5,000 residents unable or afraid to return to their homes continued to sleep in tents, temporary accommodation or cars as aftershocks continued to rattle the region.

The Italian prime minister, Mario Monti, was heckled as he visited the area after cutting short his appearance at the Nato summit in Chicago. The government declared a state of emergency for the region, with Monti promising swift help for stricken businesses, especially small farms and factories.