The chief executive of US real estate giant CoStar flew out of Australia hours before his company raised its bid to buy property listings platform Domain, offering $4.43 a share and declaring this as its best and final price.

Domain told investors on Thursday morning that its board had unanimously agreed to allow CoStar to carry out due diligence. Domain is controlled and 60 per cent owned by media giant Nine Entertainment. Nine said a sale at this price would equate to cash proceeds of $1.4 billion after tax.