A light rail carriage in Sydney has caught alight and triggered extensive delays across public transport during peak hour.

The roof of the tram was spotted on fire outside of Central Station about 8am on Thursday morning.

Witnesses reported seeing “smoke and flames coming from the roof” as it travelled between Central and Surry Hills stops, according to firefighters.

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Both the tram and the light rail station were evacuated before Fire and Rescue officers arrived to extinguish the blaze.

There have been no reports of injuries and the tram will be taken to a workshop for further investigations into the cause of the blaze.

NSW Transport has warned commuters to expect delays as both Randwick and Juniors Kingsford lines have been replaced by buses.

“The safety of passengers travelling on the light rail network is a top priority for Transdev,” the department told 7NEWS.com.au.

“We understand this causes disruption and we appreciate our customers’ patience.

“Please continue to listen to announcements, check information displays and transportnsw.info website for service updates.”