Nicola Sturgeon is to resign as Scotland's first minister after more than eight years in the role.
The Scottish National Party leader is expected to make the announcement at a hastily-arranged news conference in Edinburgh.
It is not thought that her departure will be immediate, allowing time for a successor to be elected.
A source close to Ms Sturgeon - the longest-serving first minister - told the BBC that she had "had enough."
Ms Sturgeon has been first minister since November 2014, when she took over from Alex Salmond following the independence referendum.
The first minister will hold her press conference at Bute House in Edinburgh at 11:00 local time.
Ms Sturgeon has been a member of the Scottish Parliament since 1999, and became the deputy leader of the SNP in 2004.
She then took over from Mr Salmond as leader and first minister after the defeat in the 2014 referendum.
