A pilot program allowing cross-border stock investment by investors in the Chinese mainland and Hong Kong will be subject to an initial total ceiling of 550 billion yuan ($90 billion) — 300 billion yuan for Hong Kong investors and 250 billion yuan for Chinese mainland investors, according to the China Securities Regulation Commission on Friday.

The pilot program, which was announced earlier in April, allows investors in Hong Kong to buy and sell up to 13 billion yuan of stocks in certain companies each day at the Shanghai Stock Exchange, while mainland investors may buy and sell up to 10.5 billion yuan of stocks at the Hong Kong exchange.

How long it will take to reach the pilot program's ceiling of 550 billion yuan is not known, but that limit may be adjusted depending on circumstances, the commission said.

"The values of the stock trades will be used to calibrate the limit for the pilot program," commission spokesman Deng Ge said.

Deng said other fees will not be included when calculating the limit.

Fees and taxes will be based on the standards of the stock exchanges in Shanghai and Hong Kong, and no more costs will be produced, Deng said.