The redevelopment of the Usher Hall, one of Scotland's leading concert venues, is being hit by further delays.

The A-listed auditorium, which is renowned throughout the music world, is undergoing a £30m revamp and is currently closed until the Edinburgh International Festival in August.

There are no plans to close it again after that but the City of Edinburgh Council has confirmed that the revamp is now going to take longer than it previously thought and no exact date has been set for completion, beyond a general target of spring next year.

The current delays have been caused by a need to reinforce the foundations of the building and provide additional support to some internal walls.

The Usher Hall is a key concert venue for the Royal Scottish National Orchestra and the Scottish Chamber Orchestra and any threat to their use of the hall during the winter season would be a serious blow to both.

However, the council maintained that "at this stage" their vital forthcoming winter seasons are not under threat. The reopening of the hall for the festival is also set to continue.

A council spokesman said: "The upgrading of the Usher Hall is progressing. This work means that the full project will take longer to fully complete but there is no concern at this stage over the SCO's and the RSNO's use of the venue for this coming winter season. However, we will not be taking additional bookings due to the risk of further delays and costs."