Singapore's economic slowdown might deepen and continue for a protracted period given China's deceleration, weaker trade and poor growth in the South-east Asia neighbourhood, a leading economist has warned.

This means that the stock market could fall still further, noted Bank of America Merrill Lynch economist Chua Hak Bin in a report out yesterday.

The Straits Times Index has already fallen about 20 per cent from its peak in April.

This is considerably less than the average 42 per cent decline seen in past recessions, Dr Chua said.

"The bear market is into its 22nd week, less than the average of 48 weeks in past recession bear markets."

He also noted that Singapore's small open economy has often acted as a recession barometer for the rest of Asia.

Economists have warned that the Republic likely slipped into a technical recession - two straight quarter-on-quarter declines in economic output - in the July-to-September period, dragged down mainly by a lacklustre manufacturing sector.

During the 2008 global financial crisis and 2001 technical recession, Singapore was among the first few countries to slip into recession, Dr Chua noted.

Several other Asian nations followed one or two quarters later.

The current slowdown is expected to be a "shallow recession", although there are risks that the downturn may deepen in the coming months, he added.

The current fourth quarter is expected to be the weakest quarter, but a sharper China slowdown and interest rate hikes by the United States Federal Reserve "could hurt growth and push forward the trough till the first half of 2016".

Dr Chua said that the risk of recession and a sharper downturn is also rising for the rest of Asia, especially for commodity exporters such as Malaysia and Indonesia and for markets sensitive to mainland China's slowdown, such as Hong Kong, Taiwan and South Korea.