SINGAPORE - Commuters on the Circle Line (CCL) will not get any mobile service on Friday (Nov 4) as the three telcos turn off mobile signals to enable investigations into a mysterious signal interference which had interrupted train service on Wednesday.

This means commuters will not be able to make calls, send SMS or access the Internet when travelling on the Circle Line.

The suspension of mobile services was originally meant to be for a limited period on Friday morning but was extended until further notice, Singtel, StarHub and M1 said.

The Land Transport Authority (LTA) posted an update on the "continued ongoing tests" and announced that mobile services on the CCL would be temporarily suspended on Friday.

Mobile services were also suspended on Thursday night, for more than an hour until about 10.30pm.

Train operator SMRT had earlier said that it would arrange for the suspension of mobile signals to establish whether they had caused the signal interference on Wednesday, interrupting train service for three hours during the morning peak period.

The mysterious signal interferes with the wireless signal communication between the trains and the tracks, causing the trains to apply emergency braking.

Two months ago, service on the Circle Line was interrupted by the same mysterious signal interference for a week, which disappeared before the source could be found.

SMRT said the Circle Line trains would be driven manually on Friday and that commuters should be prepared for delays.

Some commuters complained about the lack of mobile service and considered avoiding travelling on the Circle Line.

Other commuters also commented on the large crowds along the CCL, with one posting a picture of a crowded CCL station platform.

Commuters interviewed on Friday said the lack of mobile service was inconvenient and would consider avoiding travelling on the Circle Line.

Sales executive Aaron Chong, 30, was travelling on the Circle Line from Tai Seng to Bishan at about 10.45am when the train stopped at Bartley station for about six minutes. An announcement which came on said the train delay was due to an 'incident'.

He said of the mobile service suspension: "It's inconvenient if I have to get in touch with clients or if I'm expecting an urgent call."

At Buona Vista station, a 17-year-old Anglo-Chinese Junior College student who called herself Rae G. shrugged off the mobile service suspension.

"There is nothing I can do about it. These things happen. It's not like there is no service island-wide. It's a minor inconvenience."