One in every two polished diamonds from Antwerp will likely be sold to a Chinese buyer within five years, Belgian officials said on Monday as the Shanghai Expo celebrated Antwerp Diamond Day with the signing of a new memorandum between the two sides.

"China has the numbers and they are building the tradition, so (taking a 50-percent share of our market) is something that could easily happen within five years," Ludo Van Campenhout, vice-mayor of Antwerp, told China Daily.

As one of Europe's gem hubs, the city deals with half the world's output of polished diamonds, meaning that China could control at least 25 percent of the global market by 2015.

Antwerp also sees about 80 percent of the world's rough diamonds pass through the city, with the industry accounting for 7 percent of Belgium's GDP.

China overtook Japan last year as the world's second-largest market for consumer diamonds behind the United States, but it has already become Antwerp's biggest buyer, now consuming one in four of the city's polished diamonds.

"China has beaten the US as our biggest diamond market so we are very proud of the Shanghai Diamond Exchange for all its hard work," said Antwerp's governor Cathy Berx.

Berx and Van Campenhout joined other foreign dignitaries at the signing of an agreement between the Antwerp World Diamond Center (AWDC) and the Shanghai Diamond Exchange at the EU-Belgian Pavilion. The deal, called "Diamonds Love Antwerp", serves as one of the fruits of Vice-President Xi Jinping's state visit to Belgium in October.

"This is a friendship agreement between the two centers that will hopefully see China buy more from Belgium as opposed to other diamond trading centers like Israel, New York and Mumbai," said Claude Yves Nobels of the Antwerp Diamond Bourse.

"There are also a lot of things that aren't being said. There are a lot of diamonds being smuggled into China, so it's important to forge this bond to stop them coming here in an uncontrolled way that may or may not harm the public," he added.

The AWDC puts watermarks and special fibers on its diamond-validating certificates to help minimize misleading sales of synthetic gems but it wants more done to protect its interests, said its CEO Freddy J. Hanard.

"Through this unique agreement we hope to promote everything positive about the diamond trade, such as knowledge, trust, integrity and transparency," he said.

Rising personal wealth and exponential growth in demand for precious stones amid the ongoing global credit crisis has turned China into the center of the diamond-buying universe in the last few years, together with Hong Kong.