The number of companies listed on Singapore’s stock exchange has hit a two-decade low after just four companies went public this year and several delisted, with the city-state’s regulator investigating how to halt the equity market’s slide.

The number of companies on the Singapore Exchange fell to 617 in October, the lowest since September 2004. The figure has been in steady decline since hitting a high of 782 in 2013, with domestic companies attracted to overseas listings, especially in larger and more heavily traded markets such as the US.

“I surely hope that this year is a low point,” said Clifford Lee, head of the investment bank at DBS, south-east Asia’s biggest lender and Singapore’s most valuable public company. “It’s a result of various factors coming together.”