BASRA, Iraq (Reuters) - A blast hit Iraq's Umm Qasr commodities port, one of the country's largest, near the oil-exporting southern port city of Basra, two dockside workers said on Saturday.

It was not immediately clear what the cause of the blast was, or whether it had affected port traffic. The port does not export crude oil but mainly handles commodities shipments.

"A powerful blast took place at around 12.30pm near Berth 17 of Umm Qasr port shattering the windows of nearby offices," port employee Haider Abbas said.

Umm Qasr, near Iraq's border with Kuwait, sits at the top of the strategic Gulf waterway. It is close to the city of Basra, about 420km south-east of the capital Baghdad.

Imports there include grain shipments and heavy equipment used in the oil industry.