Children among dead in UK bomb attack

"This has been the most horrific incident we have had to face in Greater Manchester and one that we all hoped we would never see," said police chief constable Ian Hopkins.

The attack is being treated as a terrorist incident and was believed to have been carried out by a suicide bomber.

"The priority is to establish whether he was acting alone or as part of a network," said Hopkins.

Amber Rudd, the UK home secretary, said the "barbaric attack" had deliberately targeted young people and children.

She spoke as families were still searching for their missing loved ones and as condolences streamed in from around the world.

"Today we all express our solidarity with the victims of the terrible Manchester terrorist attack," said the British EU commissioner for security, Julian King.

EU home affairs commissioner Dimitris Avramopoulos said he was "deeply shocked" and was following developments closely.

"Our thoughts and prayers are with the victims and families of those who have been injured," said European Parliament president Antonio Tajani.

Manfred Weber, a German MEP, who leads the centre-right EPP group, said his thoughts were "with the innocent victims, their families and the UK people."

All political campaigning for the upcoming general UK elections has been suspended and the UK's prime minister, Theresa May, has called an emergency meeting.

The bombing followed terrorist attacks in Belgium, France, Germany, and Sweden over the past two years and was the second attack this year in the UK.

The fear caused by the attacks has triggered a raft of new policies and laws across EU states.

Among the largest at the EU level is the launch of the so-called Security Union, which aims to consolidate anti-terror efforts across the block's 28 member countries.

A European Commission report, published last week, set out plans on how to better share information among EU states, which includes, among others, a European search portal for the police to find suspects.

Around 2,500 EU nationals are thought to be fighting alongside the Islamic State (IS) extremist group in Syria and Iraq.

Many are likely to be killed there, and others are likely to go to other theatres of conflict, such as Afghanistan or Yemen, but some might return to Europe.

The EU's counter-terrorism chief, Gilles de Kerchove, earlier this year said that IS foreign fighters did not represent the biggest threat.

"It is rather people who live here and for different reasons can become radicals and find on the internet calls for violence and then act," he told Belgian radio in March.

He said IS was sending messages to its acolytes in Europe not to join to its so-called Caliphate in the Middle East, but to carry out attacks at home instead.