The soybeans are for shipment between January 2018 and April 2018.

Further purchases are expected, they said.

Pakistan has been a heavy buyer of soybeans from North and South America in past months. Higher import duties on soymeal have fuelled larger imports of unprocessed soybeans.

Pakistan's import duty policy is aimed at stimulating its local oilseed processing industry.

"The latest 500,000 tonnes was bought in the last ten days or so and is largely for optional US or Brazilian origin soybeans, although one or two vessels are believed to be US Gulf origin only," one trader said.

"The large volume bought shows that demand for soymeal in Pakistan from the livestock sector continues to be strong. The import duties on soymeal continue to promote imports of unprocessed beans."

The latest 500,000-tonne purchase was made in eight shipments mostly of around 60,000 tonnes each but some slightly larger. The consignments can be up to 10 percent larger or smaller than 60,000 tonnes according to the ships selected.

More soybean purchases by Pakistan are expected, traders said.

One trader said he expected a further two consignments of around 60,000 tonnes to be bought for April/May 2018 shipment.