The Exchange Fund posted its second-worst quarterly investment loss ever of HK$100.1 billion in the three months ending September, as the Hong Kong Monetary Authority (HKMA) warned of an uncertain and challenging outlook.

For the first three quarters of the year taken together, the fund that is used to back the Hong Kong dollar lost HK$265.5 billion.

Monetary officials blamed substantial losses in stocks, bonds and currencies for the slump.

In the third quarter, the Exchange Fund suffered a loss of HK$46.5 billion in equities. The investment loss in bonds widened to HK$22.8 billion from the previous quarter, while foreign exchange investments posted a deficit of HK$30.8 billion.

It is also the fund's third consecutive quarterly loss.

HKMA chief executive Eddie Yue said the investment environment this year has been unusually tough with falling valuations for equities, bonds and currency holdings.

"We might see a slight decrease in our overall losses for 2022... but because for this year as a whole up to now, both the equity market and the bond market, even with the rebound, have experienced a decrease of more than 10 percent. And the US dollar remains strong, so the chances of having a substantial loss for this year will still be there," he said.

"As for next year, it's very hard to say because the investment environment remains very uncertain and challenging. A lot depends on how the inflation data is coming out."