Meanwhile Metlink said it was also making contact with bus operators to provide stand-by buses for this afternoon's peak commute as a precautionary measure.
"We will let passengers know if we are able to source stand-by buses, but hope that high temperatures do not disrupt our services this afternoon."
Some services have already been replaced by buses on the Johnsonville line due to lack of available staff.
Water network under pressure
Wellington Water is telling residents to be mindful of their water use as hot weather baking the country enters a third day.
Acting operations general manager Jeremy McKibbin said long-term water storage levels were good, but unprecedented daily demand was putting the supply system under pressure.
"The network can struggle with refilling reservoirs overnight when there's excessive use. Of course we recognise it's hot, and using water to cool the kids off is part of what summer's all about.
"We just want people to be mindful and not waste it. Make sure water goes where it's useful. Put off washing the windows or watering the lawn for a few days until it cools down."
Water use has jumped up right across the region in Wellington, Lower Hutt, Upper Hutt and in Porirua.
Typical daily use on a warm day in the four cities is about 160 million litres but over the past three days that has jumped to more than 180 million litres a day.
Capital cracks record temperature
For about 10 minutes yesterday afternoon, the temperature in Kelburn rose to 30.3C, breaking a 90-year-old temperature record.
At about the same time a mother was relieved to have her baby back in her arms after accidentally locking it, along with her keys, in her car.
Nearby firefighters were called in for a swift rescue on Oriental Parade.
Kilbirnie station officer Peter Moffatt said by the time they arrived passersby had covered up the baby's side window with a towel.
They broke a section of the driver's side window with a hammer and screw driver to free the baby.
"The wee baby was quite red and flushed in the face so we opened the door up and mum grabbed the baby and gave it some drink and took it out of the car seat and into the shade."
"Time was an issue and I've got to say when I reached in to get that baby it was very hot inside the car."
