A scorching 34.6degC Dunedin day caused train tracks to warp and the resulting maintenance set off a 40m long scrub fire at Sawyers Bay.
KiwiRail staff were alerted to the warp in the track yesterday afternoon and sent staff to cut out a section of the track to allow it to "grow'' with the heat.
The cutting sparked the fire about 4.50pm.
Port Chalmers senior firefighter Stella Temaiharoa said it took about 10 minutes to put out but the crew remained on standby as work continued to straighten the track.
The fire was never out of control and it was the rail company's call whether to cut the track, she said.
A KiwiRail maintenance employee said they really had no choice but to cut the track as not cutting it could have resulted in a derailment.
"When it gets that hot, it just expands and buckles out,'' he said.
"The fire brigade was telling us not to cut it, but if you don't, the ... train could derail.''
The warping was detected by a heat alarm on the track, he said.
The fire, in Sir John Thorn Dr between Sawyers Bay and Port Chalmers, forced closure of the track while the Fire Service investigated and maintenance was carried out, she said.
The track was cleared and trains allowed to resume at 7.15pm yesterday..
Up to 10 train services across Otago were either delayed or cancelled due to the risk of fire, a KiwiRail spokeswoman said.
Track misalignments due to the heat also caused problems.
Dunedin City Council roading maintenance engineer Peter Standring said the heat also caused problems with roads, including State Highway 88 from Dunedin to Port Chalmers.
Tarseal melted and grit was applied to parts of the road.
"It's the sort of thing you expect on days like [yesterday]. If the seal starts bleeding, we usually put some grit on it.''
