China doubled the limit of one of the main foreign investment channels into the world's second biggest economy, continuing to open up its financial system even as the country's trade war with the U.S. jolts financial markets.

The quota for the Qualified Foreign Institutional Investor (QFII) program was increased to US$300 billion, the State Administration of Foreign Exchange (SAFE) said in a statement on Monday. It's the first expansion since July 2013, when the ceiling was raised to $150 billion from $80 billion. About $101 billion of the quota is in use by overseas institutions, according to data compiled by Bloomberg.

Authorities have been stressing that they plan to further open China's financial system, building on earlier promises that they would better integrate the more than $40 trillion sector into the global economy. Policymakers have been keen to show that the dispute with America won't derail the effort—on Friday, the banking regulator said it would study more financial-opening measures this year.