China's securities regulator unexpectedly approved 12 IPOs late on Wednesday, a move that could cool a blistering rally in the country's stock markets, which has seen the benchmark CSI index surge over 30 percent in two weeks.

The IPO approvals, reported by State media on Thursday morning, include budget carrier Spring Airlines' 1.76 billion yuan ($285 million) listing.

The move signals the potential acceleration of the pace of IPOs in the Chinese mainland, which would be good news for investment bankers, underwriters and the hundreds of firms waiting for a listing.

But it may be negative for stock indexes as analysts suspect the timing of the announcement is aimed at cooling the mainland's red-hot market.

The CSI300 index has rallied in record volume amid speculation that the central bank will further ease monetary policy to shore up the cooling economy. It fell 1.2 percent on Thursday.

That rally, which has attracted billions of fresh investor money into shares, has now given the regulator the space to accelerate the pace of IPO approval without over-diluting valuations of existing shares, especially given that many firms have seen their price-earnings valuations double in recent weeks.

But the rally has also encouraged the exuberant use of leverage as investors borrow to buy into the market, a worry for financial regulators.

Analysts said the latest round of approvals, made by the China Securities Regulatory Commission (CSRC) on Wednesday, came earlier than expected. Approvals are typically announced around the 20th of each month, so the news was seen as a potential precursor to an upcoming flood of offerings.

The 12 firms included Spring Airlines Co and medium-sized Chinese brokerage Guosen Securities, as well as a textile maker and an environmental technology services provider.

Spring Airlines said in its prospectus on Thursday it will start to offer shares on December 22 on the Shanghai Stock Exchange to raise 1.76 billion yuan. The company did not specify a reason why it had reduced a previous fundraising target of 2.5 billion yuan made in April.

The firm, China's largest budget carrier, said the funds will be used to buy up to nine Airbus A320 jets and three A320 flight simulators, as well as to supplement its working capital.

Reuters