There are still another 30 hours to go before full restoration can be expected for M1's 3G services brought down by an affected mobile network switch.

In its latest and sixth update on Facebook and its website on Wednesday, M1 said it expected its network to be fully restored only by midnight on Thursday.

"Our engineers are working flat out to restore the network," according to the notice which appeared at around 5.30pm on Wednesday.

The telco attributed the delay to the complexity of the job, which it said involves loading the configuration for every affected base station into the replacement switch. Extensive testing ensues to ensure full call continuity for both voice and data services.

The problem started at 3am Tuesday when one of its vendors was upgrading transmission equipment at network headquarters and caused a power problem. That set off gas suppression and water sprinkler systems, which tripped one of its mobile network switches, causing the loss of service.

Affected users were mainly in the south-western part of Singapore, including areas like West Coast, Jurong and Tuas. Some customers reported receiving no signal at all, while others said they had intermittent use of their devices.