The Taoiseach, Mr Ahern, has offered his sympathies to the victims of the Wellington Quay bus crash.
Mr Ahern, who visited the scene of the crash this afternoon, said in a statement: "It was with great distress that I learned about those who have lost their lives and the many others who have been injured, going about their daily lives in Dublin city centre today.
"I wish to extend my sincerest sympathies to their families at this time of terrible loss.
"Our thoughts are with the injured and their families. Our prayers are for a swift recovery for those that have been injured.
"I also wish to extend my thanks to the emergency services who all too often have to deal with tragedy of this kind."
The Labour Party's transport spokeswoman, Ms Roisin Shorthall, also sent her party's sympathy.
"The accident is all the more shocking given that buses are normally a very safe and reliable means of public transport," she said. "Clearly there must, in due course, be a full investigation into the causes of the accident and procedures put in place to prevent a similar tragedy ever happening again."
The Green Party leader, Mr Trevor Sargent, said his party was shocked at the news, and said their thoughts were with the victims.
Mr Eamon Ryan, the party's transport spokesman, also called for a review of recent proposals for the introduction of a 30 kmh maximum speed limit in the city centre.