A BUNCH of balloons have become ensnared in overhead power lines between Flinders Street and Southern Cross stations, causing major train delays as tens of thousands of people head home in the extreme heat.
The Sunbury, Craigieburn, Williamstown and Werribee lines will be stalled for at least 30 minutes while Metro technicians inspect the cables.
Other lines on the network have already been hit by major delays.
The Upfield line is suspended because of a track fault, and there are delays of about 40 minutes on the Cranbourne, Pakenham, Frankston and Hurstbridge lines.
Trains on the Cranbourne, Pakenham are Frankston lines are also bypassing the City Loop. There are reports of chaotic scenes at railway stations in the city centre as large crowds thicken on the station platforms.
Metro is also suffering a shortage of train drivers this evening after an unusually high number failed to report to work today.
Metro spokesman Daniel Hoare said the multiple track and signalling faults were not caused by today's high temperatures.
Buses have replaced trains between North Melbourne and Upfield. Commuters have been asked to defer travel if they can.