China National Nuclear Power Co Ltd (CNNPC), a unit of one of the country's two state nuclear reactor builders, said it aims to raise 13.19 billion yuan ($2.13 billion) in potentially the largest China IPO in almost four years.

The company intends to issue 3.891 billion shares at 3.39 yuan a piece, and will start taking subscriptions from investors, according to a prospectus published on the Shanghai Stock Exchange.

CNNPC is the largest of the 23 companies that will kick off initial public offerings in the first week of May. The IPOs could lock up 5 trillion yuan of liquidity, according to some analysts, and put pressure on a stock market already facing headwinds from tougher margin requirements by brokerages.

CNNPC's would be the largest A share IPO since Power Construction Corp of China's offering in September 2011.

China is aiming to raise its total nuclear capacity to 58 gigawatts by the end of 2020 from 21 GW currently, requiring huge investments.

The China Nuclear Energy Association estimates about 100 billion yuan needs to be spent every year over the next five years to meet the target.

CNNPC said its IPO price of 3.39 yuan was 22.29 times the company's 2014 earnings, which is lower than an average price/earnings ratio of 29.75 for its listed peers, including China Yangtze Power Co and GD Power Development Co.

The prospectus said it had total debt of 175.88 billion yuan at the end of last year.

CNNPC is a unit of China National Nuclear Corp (CNNC) which invests, builds and operates domestic nuclear power plants. It has 12 subsidiaries in different regions.

Last year, CNNC's major rival, China General Nuclear Power Corp, listed subsidiary CGN Power on the Hong Kong stock exchange, raising $3.2 billion.