A small number of DBS Bank's four million customers in Singapore may have problems accessing certain banking services over the weekend of Aug 5 and 6.
A DBS spokesman said the expected service disruption is due to the scale of the migration between DBS and ANZ Banking Group.
DBS last year agreed to buy ANZ's wealth management and retail banking businesses in Singapore, Hong Kong, mainland China, Taiwan and Indonesia for $110 million.
"Since the announcement of the acquisition of ANZ's retail and wealth business in five markets across Asia, DBS and ANZ have been working closely together to ensure a smooth and seamless transition. The integration is progressing well and remains on track for completion in all markets by early 2018," the bank said.
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In an e-mail to some customers, the bank said: "Some DBS services will be down from Aug 5 to 6, 2017. But we are working hard to minimise disruption."
Its spokesman said DBS sent out its first notification on the impending disruption around July 14. "We targeted customers that would likely be affected. These include active users of debit cards and Cashline. There will be another notification via SMS and e-direct mailers (eDM) at the end of the month to customers," the spokesman said.
DBS expects customer impact to be minimal as it will "continue to proactively reach out to them via SMS, eDM, as well as its online and physical channels, so they can make alternative arrangements early".
There will be no impact on key services such as Internet, mobile and phone banking, ATMs and other self-service banking channels, and the customer call centre, it said.
The service disruptions include:
• On Aug 6, from 1pm to 4pm: Debit card customers will be able to use only Nets for payment - Visa, MasterCard and China Union Pay payment will not be available. Credit cards can still be used. The bank's mobile wallet DBS PayLah! will not be available.
• On Aug 6, from 8am to 4pm: Customers will not be able to check their DBS Cashline, credit and debit card balances.
• On Aug 5 and 6: New account opening services will not be available online. DBS said records show only a handful of such transactions are performed at weekends, so it does not foresee much customer impact.
Those with queries can contact the 24-hour DBS customer service hotline on 1800-111-1111.