Temporary speed restrictions have been introduced across the entire Metrolink network due to 'severe weather conditions'.
Metrolink bosses say the precaution has been put in force to protect steel tracks and overhead lines, amid fears they could expand in the sweltering heat.
'Minor delays' are being reported on the Altrincham , Ashton , Bury , city centre , Eccles , Manchester Airport and Rochdale lines, all blamed on 'severe weather conditions'.
There are currently 'severe delays' on the East Didsbury line.
Metrolink apologised for any inconvinience.
Chris Stinchcombe, director of engineering at KeolisAmey Metrolink, said: "We are sorry if customers have experienced any delays today due to the speed restrictions in place, and thank you for your patience.
"We are experiencing very high temperatures today and to keep the network moving safely, we have reduced operating speeds, in line with standard rail operator practice.
"We are continuing to monitor the condition of the rails and overhead lines across the network to keep trams running."
Services are expected to be extra busy between 4pm and 6pm tonight.
Passengers are being advised to carry bottles of water.
Mr Stinchcombe added: "Customers are at the heart of everything we do, and we want you to have a comfortable journey experience during the hot weather.
"We expect services to be busy between 4pm and 6pm this evening and encourage customers to plan their journeys. We also advise carrying a bottle of water, and if you become unwell onboard, leave the tram at the next stop and seek help from a member of staff or by using a help-point."
On social media, Metrolink said: "Due to the current high temperatures we are experiencing, we have had to put a number of temporary speed restrictions in place across the network which may cause a delay to your service.
"We apologise for any inconvenience this may cause.
On the trains meanwhile, Network Rail announced speed restrictions would be in place on various routes until 8pm amid fears that tracks could buckle in the heat if trains travel too fast.
Speed limits on most commuter lines would be cut from 60mph to 30mph.
Extreme weather action teams have been 'activated' to keep passengers safe and trains running, Network Rail added.
Around 20,000 miles of steel track criss-crosses the country, much of which is exposed to sunlight.
According to Network Rail, which owns and manages Britain's railway infrastructure, tracks in direct sunshine can be as much as 20C hotter than the air temperature.
As the mercury rises, the steel rail absorbs heat and expands, causing it to curve, known as buckling.
The forces the temperature change provokes pushes and pulls the track out of shape, Network Rail said.
Speed restrictions due to the weather are in force around Buxton, with TransPennine Express services also said to be affected, but there are no further reported issues across Greater Manchester.
