Standard Chartered and several other banks have suspended some of their operations in central Hong Kong following mass pro-democracy protests.
Bank branches that offer over-the-counter services have been closed, as well as ATMs and cash deposit machines in affected areas.
Some firms have also advised their staff to work from home or go to secondary offices.
Thousands of demonstrators clashed with police, who fired tear gas, on Sunday.
In a statement, British bank Standard Chartered said it had activated contingency plans to ensure continuous services to customers.
Bank of China said it had suspended operations at some branches because of the "unusual situation" in parts of Hong Kong.
Singapore's biggest bank, DBS, also temporarily shuttered its branch in the Admiralty neighbourhood.
Hong Kong's de-facto central bank said 29 bank branches, offices or ATMs of 17 banks in the territory will be temporarily closed because of the protests.
The Hong Kong Monetary Authority (HKMA) said "affected banks have activated their business continuity plans this morning to maintain the normal operations of the core functions of the banking system".
"The HKMA will also inject liquidity into the banking system as and when necessary under the established mechanism," it added in a statement.
Fitch Ratings head of Asia-Pacific Sovereigns Andrew Colquhoun said the protests are unlikely to impact Hong Kong's creditworthiness "in the short term".
"It would be negative if the protests are on a wide enough scale and last long enough to have a material effect on the economy or financial stability, but we don't currently see this as very likely," he said.Political unrest
Over the weekend, thousands of protestors blocked large parts of the city to pressure the Chinese government into granting full democratic powers to the former British colony.
The demonstrators were spread across three of Hong Kong's most important commercial neighbourhoods and in front of government buildings.
Police fired several rounds of tear gas at the crowds, but the protestors continued to rally, with many staying on and sleeping in the streets.
Many of the protestors are university students who have boycotted classes since last week to hold pro-democracy rallies.
The political unrest in Hong Kong is the worst the city has seen since China took back control of the territory from the British in 1997.