(Photo: CGTN)

Leaders of European Union member states gather for a two-day informal summit on Wednesday, with cautious optimism that substantive progress could finally be made on Brexit.

The summit, which takes place in the Austrian city of Salzburg, will also feature further talks on migration, security and attempts to build bridges within the bloc.

British Prime Minister Theresa May is expected to put forward her case for the so-called Chequers plan, her proposal for Brexit which has provoked a backlash within her own Conservative Party. 

May's ultimatum on Monday that it was "my deal or no deal," meanwhile, intensified calls for a second referendum or "People's Vote."

Austrian Chancellor Sebastian Kurz gave the British prime minister a boost earlier in the week, saying that at the summit leaders "must do all we can to avoid a hard Brexit." That stance was backed by French President Emmanuel Macron and German Chancellor Angela Merkel.

Speculation last week suggested negotiations had made sufficient progress that a special Brexit summit would be announced for November. EU officials later played down the rumor, but European Council President Donald Tusk floated the possibility again on Monday evening.

"We will discuss how to organize the final phase of the Brexit talks, including the possibility of calling another European Council in November," Tusk wrote in an invitation letter to EU leaders.

The main sticking point remains the Irish border question, though reports in British newspaper The Times on Monday suggested that the EU had agreed to accept a technological solution to minimize the need for customs checks at the border.

Michel Barnier, the EU's chief Brexit negotiator, will brief the EU27 – EU leaders other than May – on the state of negotiations with only six months to go before the UK's scheduled withdrawal.

Tusk added: "Let me recall that limiting the damage caused by Brexit is our shared interest. Unfortunately, a no deal scenario is still quite possible. But if we all act responsibly, we can avoid a catastrophe."

The European Council president also addressed the issue of migration, which has returned to the top of the EU agenda in recent months and reopened tensions between member states. "I am hoping that in Salzburg we will be able to put an end to the mutual resentment and return to a constructive approach," he wrote.

Hungarian Prime Minister Viktor Orban on Monday said he would oppose an EU plan to strengthen the bloc's external borders, however, accusing Brussels of wanting to take away Hungary's control of its own frontiers.

The European Parliament's vote to sanction Hungary for breaking EU rules on democracy, civil rights and corruption could also be addressed. Orban will attend the summit a day after holding talks with Russian President Vladimir Putin in Moscow.

Security is on the agenda, while changes to EU rules on external relations could also be tackled. European Commission President Jean-Claude Juncker last week called for the bloc to adopt qualified majority voting, rather than unanimity, on some foreign policy issues.

Juncker made the proposal in his State of the Union address on September 12 as part of a broader plan to strengthen the voice of the EU on the global stage.