Shares in potash miner K+S rocketed to their highest in nearly three years after the German group revealed it had received a takeover bid from Canadian giant PotashCorp.
K+S said overnight that it had received a "written proposal" from PotashCorp for the acquisition of all its shares.
"K+S is currently assessing the available options," the German group said, adding that "this process is still ongoing".
Separately, PotashCorp confirmed that it had made a "private proposal" to K+S to "negotiate" an acquisition.
The statements sent K+S shares soaring 39% to E40.285 in opening deals in Frankfurt on Friday, topping E40 for the first time since August 2012, and adding more than E2bn to the group's stockmarket value.
PotashCorp has, reportedly, outlined a bid of E40 a share, although K+S is seen as unlikely to accept the offer.
Shares in North American groups had a chance to react on Thursday to the takeover effort, with a report appearing in Germany's Handelsblatt late in the session.
Stock in US based Intrepid Potash, also seen by many investors as a likely takeover target, soared by 10.5% to $12.16 in New York.
PotashCorp shares closed up 4.8% at $31.89 in New York.
A deal comes at a difficult time for potash producers, who have suffered a double whammy to price prospects for the nutrient.
Values tumbled in 2013 after Uralkali quit the Belarusian Potash Company consortium, undermining the price discipline in the market enforced by the cartel, and its North American peer Canpotex.
And the drop in crop prices, in curtailing farmers' enthusiasm for spending, has dented hopes for any sustained recovery in potash values.
Meanwhile, output capacity had been on an upward trend, boosted by expansions by groups such as Canada's Agrium, before an accident at a mine owned by Russia's Uralkali took out of action a site capable of producing more than 2m tonnes a year.
Uralkali itself merged with Russian rival Silvinit in 2010, to form the world's top potash miner by output.
K+S's German mines are relatively expensive to run, leaving the group particularly exposed to lower prices, although it is attempting to improve its competitiveness by opening a mine, called Legacy, in Saskatchewan, Canada, a low production cost area.
Legacy – the first mine built on a greenfield site in Saskatchewan in 40 years - is expected to start production in the middle of next year, and reach annual capacity of 2m tonnes by the end of 2017.
PotashCorp, meanwhile - which itself fended off a bid from BHP Billiton five years ago - has historically operated on the basis of taking minority stakes in a series of companies, potentially as a precursor to a full-blown bid.
The group two years ago failed in a takeover approach for Israel's ICL, of which it owns 14%.
It also owns 32% of Chile's SQM, which has this year become embroiled in a political funding scandal, plus 22% of China's Sinofert and some 28% of Arab Potash.
However, Jochen Tilk, appointed PotashCorp chief executive last year, has signalled some disquiet with some of the minority stakes.
Speaking of SQM, he said that "we do recognise that if in time there is no further expansion of that investment, then it becomes a question strategically whether or not we should hold it forever.
"And so, without putting a timeline out there, we recognise that we have to make a decision."
ICL he described as a "similar" situation, adding that "if in the long-term we are not concluding on the direction we're going, then we'll have to contemplate possibly divesting of it."