Several people have been injured in a crash between a Luas tram and a double-decker bus in Dublin city center.

The accident took place at a very busy junction in the city - between O'Connell Street and Abbey Street  - just before 3pm.

Three passengers are described as "seriously injured" while another 18 have been taken to hospital.

The tram driver and two female passengers had to be cut from the wreckage while a number of passengers were said to be "walking wounded.'

An eyewitness said that the two female bus passengers were trapped on the bus for nearly an hour after the crash.

Shoppers and tourists on the famed Dublin street started gathering at the scene,  standing around in shocked silence.

Talking to Irish, Siobhan Woods said that the Luas seemed to have hit the storage and invalid area of the bus where there are the fewest seats.

"Hopefully people were not there when the Luas hit," she said.

Traffic in and out of the city center is backed up as the main artery in Dublin has had to be closed off.

The traditional news media was slow to respond to the accident and most people found out about the crash through Twitter.

By 11.36 a.m. American time, "Luas" and "O'Connell Street" were two of the biggest trends on Twitter.

An Irish journalist tweeting under the name @UnaRocks said stayed up to date with the story by following it on Twitter - from her seat on a bus in Southern Spain.

"On a bus in southern spain following the #luas bus collision on twitter. Perfect demo of its evolving role in breaking news," she tweeted from Spain.