SINGAPORE - A power supply fluctuation that lasted only a few seconds was what led the Singapore Exchange (SGX) to shut down trading for three hours on Wednesday.

Bourse president Muthukrishnan Ramaswami said at a briefing on Thursday that the power supply to SGX's main data centre was interrupted briefly due to malfunctions in its "uninterruptible power supply" systems.

By the time power was back up, SGX could not be sure that the main data centre was in sync with the back-up data centre and made the decision to reboot both, he told a packed room.

It took some time for SGX to shut down and restart both data centres, which are located in different parts of Singapore, he added.

Trading on SGX was halted at 2.18pm on Wednesday and reopened for half an hour at 5.15pm.

Even as the SGX gave a detailed briefing, the Monetary Authority of Singapore (MAS) still asked for a more thorough investigation.

In a statement on Thursday evening it said that "takes a serious view of the trading halt experienced by SGX's securities and derivatives markets due to multiple power supply issues".

"We have instructed SGX to take immediate remedial action to prevent a recurrence. MAS has also instructed SGX to conduct a thorough investigation to find out the root cause of the outage and submit its investigation findings to MAS," an MAS spokesman said.

"MAS will not hesitate to take appropriate regulatory and supervisory actions against SGX should lapses be uncovered in the investigations," she added.