Rio Tinto has said it expects to ship less iron ore in the remainder of 2021 due to a tighter labour market that has resulted in project delays.

The world's largest iron ore producer now expects 2021 Pilbara iron ore shipments at between 320m tonnes and 325m tonnes, down from a previous range of 325m tonnes to 340m tonnes.

It blamed modest delays to the completion of its new greenfield mine at Gudai-Darri and the Robe Valley brownfield mine replacement project.