A summit called to solve the EU's migrant crisis has been plagued with division after Italy blocked a joint proposal at the last minute.

The EU's 28 leaders are gathered in Brussels for crunch talks on immigration, a debate the European Council's own president Donald Tusk admitted has become "incredibly heated."

The tensions first surfaced on Thursday evening, when a news conference to mark the summit's first day, due to be held jointly by European Commission president Jean-Claude Juncker and Mr Tusk, was cancelled after over an hour's delay.

An EU Council spokesperson blamed "one member" for refusing to agree a common position.

"No conclusions have been agreed at this stage," they said.

Diplomats later identified the country as Italy, with subsequent briefings suggesting it was holding out for a "significant" increase in funds for Africa to stem the number of migrants travelling to European shores.

An Italian government source also said it wants to overhaul the Dublin Treaty, the EU-wide law that says asylum applications must be processed in the first country migrants arrive in.

Italy, which along with Spain and Malta has received the majority of undocumented migrants docking, insisted the system had to change.

A government source from the country added it would block a deal unless all other EU leaders agreed to set up centres to take asylum seekers arriving in Europe.

The migration crisis has pushed Brexit way down the agenda at this week's summit, the last before the October deadline Britain and the EU hope a deal to be achieved by.

Brexit is on the agenda for discussion tomorrow.

A trade war with Washington, Russia, the eurozone, security and defence are all big issues on the agenda.

One senior EU official dubbed the meeting the "mother of all summits" because of the huge number of key issues up for discussion.