China's state-owned Sinochem has invited Singapore's sovereign wealth fund Temasek, to join it in a bid for Canada's Potash Corp.

Potash, the world's top fertilizer supplier, is already the target of a $39 billion hostile bid by Australian mining giant BHP Billiton.

The Canadian firm has called BHP's bid grossly inadequate, saying other parties have expressed interest.

China typically buys about 7 percent of its Potash's output and fears a BHP takeover would jeopardize its supply over coming years.

Potash shares are currently trading 15 percent above the BHP bid price, reflecting expectations of a new price for the firm.

Singapore's Temasek, which manages $134 billion in assets, has not decided if it will join the consortium bid.

Some say even if a bid is made, political opposition in Canada may prevent the Sinochem consortium's success, so it may have to add non-Chinese investors.