European Union (EU) leaders will meet at 17:00 BST for an emergency summit in Brussels to decide whether to offer the UK another delay to Brexit.
Theresa May wants to postpone the UK’s exit beyond this Friday, until June 30.
But the EU is expected to offer a longer delay, after European Council President Donald Tusk urged the other 27 leaders to back a flexible extension of up to a year – with conditions.
Mr Tusk added that “neither side should be allowed to feel humiliated”.
Leaders will begin arriving at the summit from 16:00.
Earlier, Mrs May appeared in the Commons for the weekly question session with opposition leader Jeremy Corbyn at Prime Minister’s Questions.
That head-to-head followed five days of talks between the government and Labour officials aimed at breaking the Brexit impasse.
The 1922 Committee – made up of Tory backbench MPs – will also meet at 17:00, with some members seeking a firm date for Mrs May to step down as leader of the party.
The UK is currently due to leave the EU at 23:00 BST tomorrow, April 12.
If no extension is granted, the default position would be for the UK to leave tomorrow without a deal.
So far, UK Members of Parliament (MPs) have rejected the withdrawal agreement Mrs May reached with other European leaders last year.
But the Commons has also voted against leaving in a no-deal scenario.
To prevent this happening, a group of backbench MPs managed to get a bill through Parliament to force Mrs May to ask for an extension to Article 50 – the process that defines the UK exit date – by law.
Mrs May will ask EU leaders to extend the exit date until June 30.
BBC political editor Laura Kuenssberg said the PM had to convince EU leaders about the credibility of talks with Labour and prove they were “a genuine political plan that has a chance of getting the UK out of this maze”.
Every EU member state needs to agree on any delay before it can be granted.
So, at the summit – which began at about 18:00 local time (17:00 BST) yesterday evening – Mrs May was to formally present her case for a short delay, with the option for the UK to leave earlier if her Brexit deal is ratified. –BBC