As much as four billion U.S. dollars may have moved from the turmoil in Hong Kong to Singapore, according to Goldman Sachs' report this week.

The New York-based bank estimated between three and four billion U.S. dollars in Hong Kong dollar deposits had flowed to its rival financial center Singapore as of August. 

"We found modest net outflow from HKD (Hong Kong dollar) deposits in Hong Kong and modest net inflow of FX (foreign exchange) deposits in Singapore," Goldman's analysts Gurpreet Singh Sahi and Yingqiang Guo wrote in a note to investors late Monday. 

Read More: Will Hong Kong's loss bring gains to Singapore?

Although it shows that Hong Kong banking system still has enough liquidity in Hong Kong dollars as well as in foreign currencies, "this set of data is unlikely to allay investor concerns around outflows from Hong Kong," said the analysts.

The report did not directly mention the escalating protests in the international financial hub.

The Monetary Authority of Singapore said that foreign-currency deposits by non-bank customers were up 52 percent to a record 12.8 billion Singapore dollars (1.63 billion U.S. dollars) in August. The bulk of the increase took place in both July and August, with a total five billion Singapore dollars rise in total.

However, in contrast, the Hong Kong Monetary Authority reported that Hong Kong dollar deposits declined 1.6 percent to 6.8 trillion Hong Kong dollars in August.

Poor economic outlook puts pressure on Hong Kong

In August. The Hong Kong Special Administrative Region government has lowered the GDP growth forecast for 2019 to 0-1 percent year on year. At the beginning of this year, the HKSAR government predicted that the annual GDP growth rate would be two-to-three percent.

However, the GDP growth rate of the first two quarters were 0.5 and 0.6 percent respectively.

Even though the second quarter's GDP growth rate seems firm, but it is less than expected and a seasonal adjustment has made the figure look better than it actually is.

Last month, Fitch Ratings downgraded Hong Kong's long-term foreign currency issuer default rating to "AA" from "AA+" after months of unrest, citing a negative outlook of Hong Kong.

According to Fitch, ongoing events have called into question the stability and dynamism of Hong Kong's business environment.

Recent data has also shown the city's economic performance is at its weakest since 2010, with the protests especially dealing a blow to its tourism and consumption.

(Cover image: The night view of Singapore. /VCG Photo)