Stormont First Minister Peter Robinson is standing aside, and the majority of his Democratic Unionist ministers are to resign, with party colleague Arlene Foster to take over as acting First Minister.
The surprise move from the DUP leader comes amid an Assembly crisis in the wake of a murder linked to members of the IRA.
Mr Robinson had warned that his ministers would resign if the Assembly was not adjourned or the British Government did not suspend the institutions.
The DUP step will not bring an immediate collapse of the Assembly institutions.
David Cameron is said to be “gravely concerned” by the news, with Downing Street following developments closely.