The chairman of troubled NHS Grampian has resigned after telling staff in a letter that it faced 'significant' challenges.

The health board has recently held crisis talks about staff shortages in the casualty department at Aberdeen Royal Infirmary.

Locum doctors have been employed to fill vacant posts to makes sure that the new A&E unit is run safely and there have been on-going recruitment problems.

Yesterday, chairman Bill Howatson became the second senior figure to announce his departure in recent weeks after its medical director, Dr Roelf Dijkhuizen said he is to retire.

In his announcement, Mr Howatson told staff that with the challenges that lie ahead, it was now time for someone else to take up the role.

He said: "I'm proud to have been able to play my part in bringing forward the integration of health and social care services in Grampian.

"I leave the organisation in the knowledge that we have achieved much for the people in the North East of Scotland. From delivering major capital projects and vital service redesigns to good clinical outcomes and quality care for patients.

"However it is clear that NHS Grampian still faces significant challenges and, I believe, that to give future endeavours the best possible chance of success, the health board should move forward under new chairmanship."

Mr Howatson, who joined the board as a non-executive director and has chaired it since December 2011, went onto say the board had a 'wealth of talent' and urged colleagues to get behind his successor, who has yet to be named, to deliver the best possible care for Grampian.

NHS Grampian has been facing a string of major problems over the past few months.

It launched a recruitment drive to fill vacant posts within the region earlier this year.

It came after concerned consultants questioned whether doctors at Aberdeen Royal Infirmary were able to provide safe care.

There was further controversy after a locum consultant was flown in from India to provide full weekend cover for the A&E department last month.

He was called in at short notice because the senior doctor scheduled to work the weekend shifts was off sick.

NHS Grampian previously stressed that the board was working hard to recruit new staff and admitted that there were difficulties.

With living costs rising due to the success of the booming oil and gas industry, it has proved difficult to attract new staff to the region.

Some nurses and medical staff have been forced to take on second jobs to pay high property rental costs and other bills.

In addition to this, fewer junior doctors are choosing to work in casualty departments.

With more people attending A&E units with minor illnesses, the role has become less attractive.

Health Secretary Alex Neil said he had accepted Mr Howatson's resignation, which takes place from December, and placed on record his thanks for his efforts.

He added: "NHS Grampian has made significant progress in a range of areas, for example, providing truly modern patient care in new state-of-the-art facilities and redesigning maternity services.

"Of course the board continues to face challenges as it strives to meet the needs of local people and deliver safe and effective care.

"Bill has given much to the organisation and I would like to thank him for his many years of service to NHS Scotland."