The SMRT train captain who reported tunnel flooding near Bishan station on Oct 7 also spotted electrical arcing further down the city-bound stretch of the North-South Line.

Transport Minister Khaw Boon Wan said yesterday that train captain Choo Ah Heng spotted the arcing along the tracks between Raffles Place and Marina Bay stations.

This concurrent incident, while unrelated to the flooding, also disrupted train services in both directions between Marina South Pier and Newton MRT stations from about 5.50pm.

Mr Khaw said electrical arcing occurred because accumulated debris caused a short circuit between an electrified baseplate and a bolt left in the ground after renewal works back in 2003.

The bolt should have been removed, but was not, he noted.

The short circuit generated sparks and high heat, causing the debris to smoulder. The debris quickly burned out and the sparks dissipated before the Singapore Civil Defence Force arrived.

But train services along the stretch resumed only at 9.22pm after SMRT completed the necessary safety checks, Mr Khaw said.