The Red Luas Line is down between Blackhorse and Dublin city centre.
Passengers are advised that the Red Luas Line is running only from Tallaght/Saggart to Blackhorse due to "a technical fault with the over head cables", a company statement said.
"Luas tickets are valid on Dublin Bus for the duration of the disruption. Please accept our apologies for any and all inconvenience caused."
All Green Line services are operating normally.
