A bomb that exploded in Belfast's Cathedral Quarter on Friday evening could have killed or injured anyone nearby, police have said.
The bomb exploded at Exchange Street West at about 18:45 GMT as the area was being cleared.
A warning had been phoned to a newspaper, but police said the bomb had been left in a different place.
No-one was injured by the attack, which Northern Ireland Secretary Theresa Villiers called "deplorable".
About 1,000 people were affected by the alert in the Cathedral Quarter, which is one of the main entertainment venues in Belfast, home to a number of bars and restaurants.
The Police Service of Northern Ireland (PSNI) said the bomb "had the potential to kill or cause serious injury".
"The exact nature of tonight's explosive device in the Cathedral Quarter area has not yet been established," a spokesperson added.
It is not yet known if the bomb was a small device, or a larger one which only partially exploded.
The warning call said a device had been left at a hotel in the Cathedral Quarter, but it was actually left on the footpath beside a busy restaurant, police said.
Ms Villiers said: "On one of the busiest nights of the year, with people enjoying the festivities ahead of Christmas, as well as all those in the final stages of Christmas shopping, it shows that these terrorists are stooping to a new low.
"This small minority want to drain the economic life from Belfast - but we will not let them succeed."
The Sinn Fein Lord Mayor of Belfast, M©irt©n © Muilleoir, said: "This is an attack on the community of Belfast, it's an attack on the city of Belfast, it's an attack on Christmas.
"But I think our response is that we will continue to love our city, to build our city, to enjoy our city."
Ch Supt Alan McCrum said: "This was an attack on the people of Belfast going about their normal lives on a busy night for socialising in the city.
"This attack ruined the night out for these people. Those who carried out this attack have nothing to offer except disruption and destruction."
An eyewitness, Paul Simms from Bangor, told the BBC: "I was going to see a Christmas play with my wife, 10-year-old twins and my parents at the MAC (Metropolitan Arts Centre).
"There was a police cordon set up across the road.
"I had just crossed the road to speak to a policeman by the cordon when there was a bright flash and loud bang about 40 metres away - behind a car parked beside the theatre.
"If it had been a full-on car bomb it would have been devastating.
"Needless to say my kids were scared and we were all quite shocked.
"Being typical Northern Ireland, most people just stood around hoping they could get to where they were going.
"Many had been evacuated from the bars and pubs in the area and were still full of the Christmas spirit."
Belfast City Council's emergency response department were at their Christmas dinner at a restaurant in St Anne's Square when it was evacuated before the first course.
The 20-strong team immediately went to city hall and opened an evacuation centre.
Kerry from Belfast called BBC Radio 5 live's Stephen Nolan Show and said she saw a "black Slazenger kitbag, sitting in a funny place by itself" in the area the bomb exploded when she walked past with her three-year-old son 20 minutes before it went off.
"It just has brought it home to me that I feel like I wasn't safe tonight," she said.
Leonie McDonagh from dance theatre company Ponydance had been due to perform at the MAC.
"We heard the bomb and saw some smoke, it sounded like a banger," she said.
Northern Ireland Justice Minister David Ford said: "Yet again we see a reckless attempt to kill and injure innocent people in Belfast.
"The people carrying out these attacks have set out no reason and explained no cause for their acts of senseless violence. Their only aim seems to be to injure and disrupt."
SDLP justice spokesman Alban Maginness said: "Those who perpetrated this heinous act must know that they have no support from the people of Belfast. They are anti-Belfast."
The DUP's Jonathan Craig said: "This was a reckless act which could have easily taken life or caused serious injury.
"It was a miracle that no-one was injured as the bomb exploded as the area was being evacuated."
Assembly member Basil McCrea, leader of the NI21 party, tweeted: "Caught in bomb scare at St. Anne's Square. Part explosion. Christmas festivities in Cathedral Quarter continue."
He later added: "To carry out such an act is verging on the incomprehensible. Murderous intent has been displayed and those responsible have no place in any civilised society."
Reproduced under licence from BBC News © 2013 BBC