When Zhou Weixia left her job as a bank clerk to conduct sapphire trading with her husband, she had no idea the price of the local stone would skyrocket more than 50 times over the last decade.

But now the 28-year-old from Changle county in East China's Shandong province, one of the world's major sapphire production areas, is seeking opportunities to buy and store as much sapphire as possible, betting that the price will keep increasing to a new high in coming years.

"I paid 20,000 yuan ($3,175) in 2007 for a 24-carat sapphire and I refused to sell it when someone offered 400,000 yuan just a few days ago," said Zhou, dressed in a luxurious fur coat, as she pointed at a sparkling blue stone.

"It's very hard to find such a fine star-sapphire (a rare type of gem displaying a pattern of stars) now. The price will stay high. I won't take less than 700,000 yuan," Zhou said.

Ten years ago the average price of a one-carat sapphire was only dozens of yuan on the local market, but now a one-carat general sapphire may cost 2,000 to 5,000 yuan and high quality stones cost at least a five-digit figure for each carat, according to Zhou.

The jewelry store she ran with her husband for more than 10 years is making an annual turnover of 10 million yuan now.

Zhou isn't the only one in Changle who has made a fortune out of the precious stone. Sapphire trading has created a handful of millionaires and even billionaires in the small county town.

About three hours drive from Shandong's capital city Jinan, Changle is one of the few places in the world with rich sapphire reserves. Its sapphire is characterized by large size, intactness and purity of color. There are also main features that distinguish it from those of other producing areas in the world, such as Thailand and Sri Lanka.

However, local people treated the dark-blue gem as valueless ordinary stones until 1986, when the region was found to boast 450 square kilometers of sapphire-rich land with deposits totaling more than one billion carats.

Since then, gem dealers and collectors from other parts of the country and even from abroad started appearing in the county and tried to buy rough sapphire deposits in bulk at incredibly low prices. The region soon became a collection of privately-owned mines.

"At first we didn't know much about sapphires and we were just so glad that someone wanted to pay for them," said Liu Hongchang from Wutu village. He began to dig for the stones with his fellow villagers in 1999.

The local government started to place restrictions on exploration from 2008 and banned any form of mechanized mining last year, citing concerns about national resource protection. It significantly reduced production and caused the price of sapphires to shoot up.

"There is little supply now. The scarcity makes it more valuable. If the same bag of deposits were sold it would cost at least several million yuan," Liu said, rueful that he had let go some precious stones too early and too easily.

To improve the fame of its sapphires, the county has held a string of promotions across the world in recent years, including the 2010 Press Conference for International Sapphire Fashion Trends in Hong Kong and the Cross-Straits Cooperation and Development Forum for Jewels in Taiwan.

Thanks to these activities, a large number of fine sapphires from Changle have caused a stir among jewelers around the world. They include a 760-carat sapphire in the shape of a drop of water exhibited at the 2010 Shanghai Expo and a 1,764.8-carat stone shown in Hong Kong. It is one of the largest of its kind in the world.

"Increasing numbers of jewelry lovers find themselves attracted to our sapphires and collect them. Some wealthy investors even buy them for speculative reasons because the stock market and real estate are no longer returning the profits they once did," said Cheng Xiaopeng, vice-general secretary of the Changle Jewel and Jade Industry Association, explaining another reason for their rise in value.

However, although the price of sapphires from the county has rocketed in recent years, Cheng said the price is still significantly lower than the international market price.

"For quite a long time, about 60 percent of sapphires in the county have been exported to other countries, such as Thailand and the United States, where the price will double, sometimes even triple," Cheng said.

Sapphires, along with diamonds, rubies and emeralds, are regarded as the world's top four valuable gemstones. They have long been popular among Western people, especially members of European royal families, who regard them as representations of love and faithfulness. A point in case is Prince William, who proposed to Kate Middleton with an 18-carat oval blue sapphire ring, which was his mother Diana's engagement ring.

"Sapphires do not share the same cultural identity in China as they do in the West. They are mainly bought by jewelry lovers and collectors. The majority of Chinese customers do not acknowledge their cultural value as they do for jade and diamonds," said Shi Hongyue, vice-general sectary of the Jewel and Jade Industry Association of China.

"Hotan jade prices have increased about 5,000 times in China over the same 10 years. Once ordinary people take to sapphires, their price will be quite different," said Shi, indicating the vast potential market.

To help more people know about the precious stone, an annual international sapphire festival has been held in Changle for 10 years.

The local government has also unveiled a range of favorable policies to stimulate the local jewelry industry, including startup funds, financial services and tax discounts.

A large gemstone processing and trading center - the Gem City of China - has been built. It is the only one of its kind named by China's State Administration for Industry and Commerce.

The center has attracted more than 200 leading jewelry companies from Beijing, Shanghai, Shenzhen, and Hong Kong, which promote the industry's growth. Changle has now established a complete jewelry industry chain from sapphire prospecting, mining, refining and processing to jewelry product trading.

The county has more than 2,000 companies involving in sapphire manufacturing, processing and trading. They can produce a total of 13 million carats annually, bringing in 36 billion yuan in trading volume, figures from the local authorities show.

An ambitious plan has been developed that involves the establishment of 2.6 million square meters of jewelry manufacturing and processing center with an annual turnover of 100 billion yuan by 2015.