An international design competition for a multi-million pound overhaul of Aberdeen's Union Terrace Gardens has been given the green light by local councillors.

Aberdeen City Council (ACC) backed proposals to move forward with the City Square Project, having already approved an offer worth £50m towards the scheme from businessman Sir Ian Wood. Designers and architects from around the world will soon be invited to submit ideas for the gardens project, with Sir Ian contributing up to 50 per cent of the competition costs.

The £140m development will include reclaiming 5 acres (22 hectares) of land by raising the site and covering a dual carriageway, a cultural hub and an outdoor performance stage. Water features that recognise the importance of Aberdeen as a major North Sea port, an amphitheatre and green space are also proposed as part of the project.

ACC leader John Stewart said: "We have taken no final decisions. All we are doing is moving on to the next stage in the process. If the council is not happy at any stage, we can pull back. If the finances are not right, we can call a halt. "Clearly there are risks - and what we have to do now is assess and evaluate them. The only way to do that is move forward to the next stage of the project. To stop now would leave us all wondering 'what if'."

A project management board will be established to provide strategic leadership in the development's early stages, which will comprise two ACC councillors and representatives from a number of organisations.