Beijing's People's Bank of China said it "firmly supports Huijin Investment... in increasing its holdings of stock market index funds".

It promised to provide the fund "with sufficient re-lending support when necessary, resolutely maintaining the smooth operation of the capital market".

US President Donald Trump upended the world economy last week with sweeping tariffs that have raised fears of an international recession and triggered criticism even from within his own Republican Party.

As the trade war escalates, Beijing -- Washington's major economic rival -- unveiled its own 34 percent duties on US goods to come into effect on Thursday.

Trillions of dollars have been wiped off combined stock market valuations in recent sessions.

Hong Kong collapsed by 13.2 percent Monday, its worst day in nearly three decades.

As markets tumbled, Central Huijin Investment vowed to help ensure "stable operations" of the market with a share buy-back programme.

In a statement, the firm said it "has once again increased its holdings of exchange-traded funds and will continue to increase its holdings in the future".