Much of the massive Chinese purchases of commodities in recent weeks have gone to stockpiles rather than to satisfy current demand.

That means the huge Chinese buying is unlikely to continue, and that in turn means commodity prices may be unable to sustain their recent advance.

As for the stockpiling, at least 90 freighters stuffed with iron ore that are floating at China’s ports will have to wait as much as two weeks to unload their cargo because port storage facilities are full, shipping company executives tell The New York Times.

The Chinese have been hoarding everything from oil to aluminum to copper to canola and soybeans.

The oil buying has helped push prices above $70 per barrel.

“There has been enormous stockpiling of all commodities” by China, but that can’t continue indefinitely, Tim Huxley, chief executive of Wah Kwong Maritime Transport Holdings, tells The Times.

Some even say the China buying represents a commodities bubble.

“The past two weeks have been nuts and, rather than cheering this sudden comeback of the dry bulk market, I do have a considerable amount of concern that we are seeing the same bubble again,” Kenneth Koo, chief executive of Tai Chong Cheang Steamship Co., tells The Times.

But some experts remain bullish on commodities for the long term.

“I know we’re in a secular bull market for commodities,” investor Jim Rogers tells Moneynews.

“Things are going on that are good for the fundamentals of commodities.”