The Hong Kong Stock Exchange on Wednesday bid almost £32 billion for its London rival to bring together the largest financial hubs in Asia and Europe, it said Wednesday.
The blockbuster proposal including debt, worth $40 billion or 36 billion euros, is dependent on the London Stock Exchange Group (LSEG) scrapping a proposed $27-billion takeover of US financial data provider Refinitiv.
In reaction, LSEG said it would "consider the proposal" but stressed that it "remains committed" to buying Refinitiv.
The surprise news sent LSE shares surging 6.3 percent to about £72, but far below the offer price of more than £83 per share.
London's benchmark FTSE 100 index was up 0.9 percent overall in late morning deals.
"Hong Kong Exchanges and Clearing Limited (HKEX) today announces that it has made a proposal to the board of LSEG to combine the two companies," it said in a statement.
The cash-and-shares is worth £31.6 billion including £2.0 billion of debt, HKEX added.
The Hong Kong company said a deal would leave the combined group "ideally positioned to benefit from the evolving global macroeconomic landscape, connecting the established financial markets in the West with the emerging financial markets in the East, particularly in China."
HKEX chairman Laura Cha said a deal represented a "compelling" opportunity.
She added: "We believe a combination of HKEX and LSEG represents a highly compelling strategic opportunity to create a global market infrastructure group, bringing together the largest and most significant financial centres in Asia and Europe.
"Following early engagement with LSEG, we look forward to working in detail with the LSEG board to demonstrate that this transaction is in the best interests of all stakeholders, investors and both businesses."
The gigantic takeover tilt comes just one month after the LSEG had embarked upon a vast takeover of Refinitiv, in a move that would have created a market information giant to rival US titan Bloomberg.
The deal remains subject to approval by both sets of shareholders, as well as the termination of the Refinitiv deal.