Regulators in the east China province also ordered a recall of all the "zongzi" made by Wan Maomao Frozen Food Co, as it is difficult to tell the old from the new.

The company's sales of the sticky-rice snack are "considerable," Xinhua news agency reported, without specifying a figure.

In addition to more than two tons of expired "zongzi" discovered at the company in a weekend raid, authorities retrieved 1.4 tons of the product that had been sold across the province. There was no evidence that any had made its way out of Anhui.

"Zongzi" is a traditional Chinese snack that's eaten during the Dragon Boat Festival, which begins today.

The festival commemorates the ancient patriotic Chinese poet Qu Yuan (340-278 BC). Legend has it that Qu drowned himself in a river and people threw in "zongzi" to keep the fish from eating his body.

The main ingredient in "zongzi" is glutinous rice. It is stuffed with meat or other fillings and wrapped into a triangular shape with bamboo or reed leaves.

The problem product was discovered in the Wan Maomao workshop by the Administration of Quality and Technical Supervision in Hefei, Anhui's capital, after receiving a tip.

Authorities found a large number of old "zongzi" had been ripped out of the original bamboo leaves and rewrapped with fresh leaves. The original packaging showed it was produced in 2005.

The rice in the leftover products had turned milky white, and some had already started to rot, giving off a bad smell.

Eating the expired snacks could cause food poisoning, experts said. The company also received a warning from the quality supervision authority in May last year for producing "zongzi" that had quality problems, officials said.