At 15:05, a power trip occurred on Hong Kong Island and affected the electricity supply to SEHK's computer room in Exchange Square. The Exchange's Uninterrupted Power Supply system (UPS) was automatically triggered to substitute the city power. AMS was able to continue its normal operation with the UPS cut-in. The UPS also activated its alarm bell to signal a power interruption.

While deactivating the alarm bell, it was reported that the Emergency Stop function of the UPS system was accidentally triggered. This cut off power supply to the AMS host computer, all trader PCs in the trading hall, and the off-floor trading terminal telecommunication facility.

The Tandem host computer was at that time in operation mode and internal battery power of Tandem was used. The Exchange received reports from members that the second and third terminals had blacked out.

The floor manager announced in the trading hall that the interruption was due to power supply failure.

At around 15:10, members of the Contingency Management Team (CMT) of the Exchange were assembled. Various parties and regulators were being informed of the situation. The UPS was also reactivated.

At around 15:30, CMT continues to assess the recovery of trading terminals. At the same time, first terminals in the Trading Hall began to re-establish their AMS connection automatically. Progressively, over 90 per cent of the first terminals completed their AMS connection automatically.

Hong Kong Telecom was requested to reset the network equipment to effect connection of the second and third terminals. The Second and Third terminals, the off floor trading terminals, recovered progressively.

The CMT decided not to extend trading hours and allowed AMS to close the market at 16:00 as normal market close and to inform various parties including regulators.

An announcement was made at the trading hall to advise members that the market would close at 16:00 as normal. At the same time, the same message was sent to members through pagers, email and Teletext News.

At 16:05, traders reported to the floor manager that the system was still on. It was found that AMS was unable to stop the market at 16:00 and trades were executed until 16:05.

At around 17:30, Examination of the AMS database integrity was completed. It was concluded that 1,099 trades (0.46 per cent of total) amounting to a turnover value of HK$107,624,667 (0.58 per cent of total) and 80,290,002 shares (0.43 per cent of total) occurred during the 5 extra minutes.

An announcement was made to the market that trades executed after 16:00 would not be recognised by the Exchange.

The accuracy of the trade data and closing prices recorded in AMS were verified, and end-of-day trading record files were released to members electronically

Remedial measures were taken by the Exchange after yesterday's incident. Among these measures, the Exchange will review and strengthen the operation procedures and computer operation system to prevent future happening of similar incidents.