THREE years ago Peter Hart's busy grain storage and container packing business on Queensland's Darling Downs was just testing the market for cotton seed exports - now the fluffy grey pellets dictate about half the site's workload.

This year Grainhart at Oakey expects to pack about 70,000 tonnes of cotton seed mostly drawn from gins in North West NSW.

About 85 per cent of Grainhart's shipping container loads are destined for China.

"The Chinese demand just came out of the blue, said Mr Hart, whose company loads 12-metre long (40 feet) food grade containers for about five exporters.

The 24 to 26 tonne consignments are treated for insects before loading, then trucked to Brisbane on the first leg of a three week journey to one of four main Chinese ports.

"It's very busy at the moment," said Mr Hart.

He started out storing grain before diversifying into container packing nearly five years ago and now packs almost 200,000t of cereals and pulses a year for markets as diverse as Papua and New Guinea, Thailand and New Zealand, plus the cotton seed.

"At this time of year we could handle a few more packers in the game but then for four to six months we're sitting around waiting for things to get hectic again."

Mr Hart's biggest concern is sourcing enough containers to keep up with the cotton seed volumes being loaded, with his company's trucks frequently in Sydney and Melbourne collecting empty containers to take north.

Queensland Cotton senior trader Ian Grellman said cotton seed required the biggest possible boxes because the product was relatively light and inesfficient to move in smaller 16t capacity units.

The container scramble was made even harder than normal because cotton bales were also shipped in 12m boxes and with so much cotton to export demand for storage was hot.