"8 fire engines, advanced paramedics and other specialist appliances are now attending the fire in Ballymun," Dublin Fire Brigade tweeted.
The Irish national broadcaster RTE said the blaze at the Metro Hotel is believed to have started after 19.30GMT.
This is a bad one…Metro Hotel,Ballymun Dublin, pic.twitter.com/7zQbc8Jv6p
— Tomas (@coady327) March 21, 2018
Dublin hotel fire: Guests evacuated from Metro Hotel in Ballymun https://t.co/4yISB8H15O pic.twitter.com/RE1aRUfWTN
— Siglov Freudivan (@DerangedRadio) March 21, 2018
Photos posted in local newspapers show flames erupting from at least two floors of the multi-storey building.