THE Stormont Assembly election will take place on March 2, the Northern Ireland Secretary has announced.

James Brokenshire called the poll on Monday minutes after a deadline elapsed that effectively triggered the collapse of the powersharing executive in Belfast.

Mr Brokenshire was obliged by law to set an election date after Sinn Fein brought down the institutions by refusing to replace Martin McGuinness as deputy first minister.

Mr McGuinness quit last week citing irreconcilable differences with his long-term Democratic Unionist partners in government.

The deadline for Sinn Fein to re-nominate a minister passed at 5pm on Monday.

At the start of Assembly business on Monday, Sinn Fein declined to replace Martin McGuinness as deputy first minister a week after he quit citing irreconcilable differences with his long-term Democratic Unionist partners in government.

His resignation was precipitated by the renewable heat incentive (RHI) scandal - a botched eco-scheme set to cost Stormont £490 million - but that row has also reignited a range of other bitter disputes dividing the coalition.

Sinn Fein MLA Michelle O'Neill told the Assembly: "The DUP have treated these institutions and sections of the community with contempt and arrogance.

"Today, Sinn Fein will not re-nominate for the position of deputy first minister."

Ms O'Neill said Sinn Fein would only return to government if there was "real and meaningful change".

Mr McGuinness's resignation automatically removed DUP leader Arlene Foster from her position as first minister - as executive structures dictate one cannot govern without the other.

On Monday, the DUP renominated Mrs Foster to the post. That was rendered meaningless by Sinn Fein's subsequent refusal to renominate its own incumbent at the head of the executive.

Speaker Robin Newton said both ministers needed to be in post for their office to function.

"These requirements have not been satisfied today and the offices of the first minister and deputy first minister must remain vacant," he said.

Ahead of the key Assembly session at Parliament Buildings in Belfast, Mrs Foster said the electorate did not want or need an election.

She accused Sinn Fein of triggering a poll because they did not like the outcome of last May's vote.

"They have forced an election that risks Northern Ireland's future and stability, and which suits nobody but themselves," she said.

Theresa May phoned Mrs Foster and Mr McGuinness early on Monday in a last-ditch effort to prevent the collapse of the devolved administration.

The Prime Minister's official spokeswoman said Mrs May wanted to make sure Northern Ireland has "a voice" in the run-up to the start of EU withdrawal talks - expected to be triggered by the end of March with the invocation of Article 50 of the European Union treaties.

The Stormont Assembly will limp on until it is formally dissolved. An election is likely in late February or early March.