DONGYANG, China, March 29 (Reuters) - It’s the end of a school day in the eastern Chinese city of Dongyang, and eager parents collect their children after a hectic day of primary school.

But that’s just the start of busy times for dozens of egg vendors across the city, deep in coastal Zhejiang province, who ready themselves to cook up a unique springtime snack favoured by local residents.

Basins and buckets of boys’ urine are collected from primary school toilets. It is the key ingredient in “virgin boy eggs”, a local tradition of soaking and cooking eggs in the urine of young boys, preferably below the age of 10.

There is no good explanation for why it has to be boys’ urine, just that it has been so for centuries.

The scent of these eggs being cooked in pots of urine is unmistakable as people pass the many street vendors in Dongyang who sell it, claiming it has remarkable health properties.

“If you eat this, you will not get heat stroke. These eggs cooked in urine are fragrant,” said Ge Yaohua, 51, who owns one of the more popular “virgin boy eggs” stalls.

“They are good for your health. Our family has them for every meal. In Dongyang, every family likes eating them.”

It takes nearly an entire day to make these unique eggs, starting off by soaking and then boiling raw eggs in a pot of urine. After that, the shells of the hard-boiled eggs are cracked and they continue to simmer in urine for hours.

Vendors have to keep pouring urine into the pot and controlling the fire to keep the eggs from being overheated and overcooked.

Ge said he has been making the snack, popular due to its fresh and salty taste, for more than 20 years. Each egg goes for 1.50 yuan ($0.24), a little more than twice the price of the regular eggs he also sells.

Many Dongyang residents, young and old, said they believed in the tradition passed on by their ancestors that the eggs decrease body heat, promote better blood circulation and just generally reinvigorate the body.

“By eating these eggs, we will not have any pain in our waists, legs and joints. Also, you will have more energy when you work,” said Li Yangzhen, 59, who bought 20 eggs from Ge.

The eggs are not bought only at street stalls. Local residents are also known to personally collect boys’ urine from nearby schools to cook the delicacy in their homes.

The popularity of the treat has led the local government to list the “virgin boy eggs” as an intangible cultural heritage.

But not everyone is a fan. Chinese medical experts gave mixed reviews about the health benefits of the practice, with some warning about sanitary issues surrounding the use of urine to cook the eggs.

Some Dongyang residents also said they hated the eggs.

“We have this tradition in Dongyang that these eggs are good for our health and that it would help prevent things like getting a cold,” said Wang Junxing, 38. “I don’t believe in all this, so I do not eat them.” (Editing by Elaine Lies and Paul Casciato)