Scotland's transport minister has quit the government amidst ongoing issues over the country's ferry services.

Kevin Stewart MSP penned a resignation letter to First Minister Humza Yousaf, saying he had been struggling with low mental health since October last year. 

The Aberdeen Central MSP added that he had been feeling unwell for the past week, and could not put in the hours required to serve his constituents and hold a ministerial position.

Mr Stewart wrote: "Since last October I have had bouts of poor mental health, with a low ebb in early December of last year.

"Over the last week or so I have one again been feeling unwell and I feel that I can no longer put in the hours required to serve both my constituents and hold ministerial office, while also trying to maintain good mental health."

"It has been the honour of my life to serve the people of Scotland in three ministerial positions under the leadership of Nicola Sturgeon and yourself and I do hope that I have made a positive difference for our people and our country".

The SNP MSP will continue to serve as an MSP, with the First Minister saying he was sory to see him go.

Humza Yousaf said: "I know what a hard-working, loyal and dedicated minister you have been in your eight years of service.

"That is much valued by me and across government, and I hope you will feel able to serve again in the future".

The First Minister also said that many people underestimate the pressure that is put on government ministers, and offered Mr Stewart any support that he needed.

Mr Stewart was appointed to the role in March, taking over from Jenny Gilruth as the face of Scotland's ferry transport issues. 

That includes the ongoing problems with the future Glen Sannox and Hull 802 vessels at Ferguson Marine in Port Glasgow. 

The vessels, which are several years late and millions of pounds over-budget, are needed to provide relief across the CalMac network. 

Issues with ageing fleets and lack of capacity has also dogged routes such as those between Largs and Cumbrae.

He was then given the transport brief by Mr Yousaf, when the new First Minister unveiled his government team in March of this year, with his role including ministerial responsibility for Scotland's struggling CalMac ferry fleet.