CSL, one of the world's top five biotech companies, and Sigma Pharmaceuticals have their headquarters in Melbourne. The two are the largest listed Australian pharmaceutical companies. Melbourne has an important ICT industry that employs over 60,000 people (one third of Australia's ICT workforce), with a turnover of $19.8 billion and export revenues of $615 million. In addition, tourism also plays an important role in Melbourne's economy, with about 7.6 million domestic visitors and 1.88 million international visitors in 2004. In 2008, Melbourne overtook Sydney with the amount of money that domestic tourists spent in the city, accounting for around $15.8 billion annually. Melbourne has been attracting an increasing share of domestic and international conference markets. Construction began in February 2006 of a $1 billion 5000-seat international convention centre, Hilton Hotel and commercial precinct adjacent to the Melbourne Exhibition and Convention Centre to link development along the Yarra River with the Southbank precinct and multibillion-dollar Docklands redevelopment.