One of Scotland's most popular festivals looks set to increase its ticket sales as music fans flock to the Outer Hebrides from across Scotland – and the world.

The 18th annual Hebridean Celtic Festival opened last night in Stornoway, Isle of Lewis, with singer Van Morrison headlining tonight and a line-up also featuring Dougie MacLean, Capercaillie, The Battlefield Band and the Red Hot Chilli Pipers.

Caroline MacLennan, the director of the four-day festival, said that ticket sales have surpassed last year's total of 14,000 and local sales have not yet been added, with more tickets to be sold.

She said the festival, which is run with the help of 150 volunteers, has become a powerful force in the local economy.

In a study of 2011 ticket sales, 54% were sold to residents of Lewis and Harris, 3% were from elsewhere in the Outer Hebrides and around 30% resident in the rest of Scotland, with 8% resident in the rest of the UK.

Around 5% of fans came from outside the UK – a pattern repeated this year.

The events generated total economic impact of approximately £887,000 and a recent Audience Research report found that 57% of visitors stated that their sole or main purpose for visiting the Outer Hebrides was to attend the festival, with more than a third of visitors travelling to the Outer Hebrides for the first time.

The festival supports the equivalent of 37 full time equivalent jobs.

"It really has become a major part of the economy, not only for accommodation but for businesses like furniture shops selling beds for extra visitors," she said.

"I still think there are a lot of people who have yet to find out about the festival, but the coverage on BBC Alba has really helped and raised our profile in the last few years.

"We are already looking forward to 2014, which is of course the Commonwealth Games year and 2015 is our 20th anniversary."

An appeal for local people to make available accommodation to the influx of visitors was made in April – two months earlier than usual – due to the demand.