Auction houses have sold $700 million-worth of artwork in recent days in Hong Kong and set a series of world records, as Asia's art market heats up anew and competition mounts between Chinese and foreign firms.

Western giants Christie's and Sotheby's are increasingly focused on China but barred from selling the hottest item -- antiques -- by laws aimed at protecting cultural heritage.

Meanwhile Chinese rivals Poly and Guardian have seen tremendous growth thanks to their greater freedom to act within the country, and their political ties.

And now they are seeking to challenge foreign competitors outside the mainland.

So far they have been encroaching on Western art traders' turf in Hong Kong, the former British colony turned semi-autonomous Chinese city.

They held their most ambitious sales in Hong Kong so far last week, timed to capture an influx of well-heeled Chinese during a week-long national holiday.

Still, Sotheby's, which is marking its 40th year in Asia, managed to hold on to the lion's share of the market -- and the headlines -- with some exceptional items.

A white diamond sold for $30 million, breaking a world record; a Zeng Fanzhi painting that went for $23 million set a new record for a contemporary Chinese artist; and a gilt bronze Sakyamuni Buddha did the same for Chinese statues, selling at $30 million.

The figures represent regained momentum for the Chinese art market after an unexpected contraction last year, when New York reclaimed its place from Beijing as the world's lead city for art sales.

China still led global arts and collectibles auction revenue in 2012, according to the French Conseil des Ventes Volontaires.

Auction houses have been ramping up their pursuit of China's burgeoning millionaire class.

"Their first priority is to gain direct access to the wealth of the mainland Chinese, much of which wealth is contained within the borders of the country," said Nancy Murphy, a lawyer and expert on the Chinese art market.

"Right now, the vast majority of Chinese art money is chasing only Chinese art; Western art dealers are very, very interested in working to expand that demand, and bringing more Western art physically into China is an excellent first step."

"China is in buying mode"

London-based Spink and Son, founded in 1666, recently moved its president to Hong Kong, to "further galvanise Spink's thriving Asia business", it said in a statement.

After years of waiting, in late September Christie's held its first auction in mainland China in the commercial hub Shanghai.

Sotheby's will hold its second in December in Beijing, with a feature piece from French-Chinese artist Zao Wou-Ki, who died in April.

But Meg Maggio, an American gallery owner with 20 years' experience in China, believes Western firms will not flourish on the mainland -- and at best they might attract more buyers to New York, London and Paris.

"They have to come because what else can they do? They've basically lost their dominance in Hong Kong," she said.

"I think their growth will be minimal."

She said the art market is "primarily" older items -- where Chinese law gives domestic companies a huge advantage.

They also benefit from important political connections.

Poly Auction, the third largest house in the world, belongs to a state-owned conglomerate controlled by the army and headed by the son-in-law of China's former leader Deng Xiaoping.

Chen Dongsheng, cofounder of Guardian, the world's fifth largest auction firm, is married to the granddaughter of the late leader Mao Zedong.

The director general of Poly Auction, Zhao Xu, has been quoted in Chinese media as saying the arrival of foreign firms did not worry him, given the legal framework.

It is unclear if Beijing will ever lift the prohibitions on foreign auction houses, although Murphy expects they will gradually ease, allowing healthier competition.

Meanwhile Chinese firms trying to make inroads outside their country may enjoy swifter success.

With a huge publicity drive they have sought to convince Western collectors to buy and sell through them, and Poly has opened an office in New York.

"China is definitely in buying mode," Maggio said. "The Europeans and other people are more in the selling mode."