M1's 3G mobile services were disrupted for about three hours on Wednesday morning in the western and north-western parts of the island. Services were restored as of 9.15am.

The telco said on its Facebook page that some customers including those in Yishun, Jurong, Woodlands and Choa Chu Kang were experiencing service difficulties. It however did not specify a reason for the outage.

Many frustrated customers posted on its Facebook page complaining that they could not make calls or use messaging services such as Whatsapp. "No network in Choa Chu Kang.. can't call out, Can't use data plan... it's causing us inconvenience," wrote a user by the name of Michelle Choo.

The Straits Times understands that this service outage is not linked to last week's SingTel fire which disrupted fibre broadband Internet, pay-TV, fixed and mobile voice services, as well as essential services such as banking, for hours.

Earlier this month, M1 was fined a record $1.5 million for a service outage in January which lasted up to 71 hours, affecting some 250,000 M1 users - the worst mobile network failure Singapore has experienced to date.

That outage affected 3G services in the south-western parts of Singapore (West Coast, Jurong and Tuas) and 2G services in the north-western parts of Singapore (Woodlands, Yishun and Kranji). It occurred when one of its vendors was upgrading transmission equipment at its network headquarters in the International Business Park.

This caused a power problem which set off gas suppression and water sprinkler systems. One of the telco's mobile network switches then tripped, causing the outage.