A van was reportedly hijacked and driven to the venue, and a controlled explosion has since been carried out.
Irish Foreign Minister Simon Coveney has been evacuated from a building in north Belfast amid a security alert.
He was giving a peace-building talk at the Houben Centre on the Crumlin Road, when a van was reportedly hijacked and driven to the venue.
Mr Coveney said he was “saddened and frustrated someone has been attacked and victimised in this way”.
An MP said it was understood the van had been loaded with “explosives or something purporting to be explosives”.
The BBC’s Ireland correspondent Chris Page said a controlled explosion had been carried out at the scene at about 13:00 GMT.
The alert also disrupted a funeral at nearby Holy Cross Church, which was then held in the church carpark.
Image source, Pacemaker
Mr Coveney had been at the podium for just five minutes when his security officer ushered him off the stage. He apologised and left quickly.
SDLP MP Claire Hanna, who was at the event, said they were told a hijacked van, with potentially a suspicious device on board, had been found in the area.
“People are frustrated,” she said.
“The irony is lost on nobody that this was an event about reconciliation, about common ground with a genuinely diverse audience of people.
“That it has been disrupted in such an aggressive way is appalling”.
Police have advised motorists to avoid the area and seek alternative routes.
In Belfast with @Humefoundation to honour John & Pat’s legacy of peace for all communities. Saddened & frustrated that someone has been attacked & victimised in this way and my thoughts are with him & his family. My thanks to @PoliceServiceNI https://t.co/bs9LvTKBHW
— Simon Coveney (@simoncoveney)
About 100 people, including a number of politicians, were at the event.
Ulster Unionist assembly member Mike Nesbitt, who was among the guests, said: “I am ashamed and disgusted in equal measure at the people who did this.
“A driver going about his daily business is now traumatised god knows how badly. What are they thinking?”
Sinn Féin MP John Finucane said the hijacked van had been left on church grounds.
He said those behind it “had no place in society”.
“While they try to bring back the past, we will keep working for the future,” he added.
Image source, Pacemaker
Prof Colin Harvey, who teaches human rights law at Queen’s University in Belfast, said he had been looking forward to the opportunity to “hear from Simon Coveney about building common ground” before the speech abruptly ended.
“My view is, people need to wise up,” he said.
“People want peace in this society and this needs to stop.”
Northern Ireland Secretary Brandon Lewis tweeted that he was in “solidarity” with Mr Coveney and all those affected.
The event had been organised by the John and Pat Hume Foundation, which was established in honour of the Nobel Peace Prize winner John Hume and his wife.
The foundation’s Tim Attwood said the alert was a reminder “to everyone that there is no role in our society for violence”, RTÉ has reported.
The Houben Centre is located at the interface of the Ardoyne and Shankill – it operates as a cross-community centre and also the parish centre for the Holy Cross church.