HKEX's offer values LSE at £83.61 a share, a 23% premium to LSE's closing price on Tuesday. LSE shares climbed as much as 16% before paring gains to trade 5.9% higher after HKEX made its surprise $36.6 billion bid for the UK-based exchange group. LSE later said in a statement that it "remains committed to" its proposed acquisition of Refinitiv.  

If the deal were to be completed, it would be by far the largest in the history of HKEX, which previously bought the London Metal Exchange for £1.4 billion in 2012.

"Bringing HKEX and the London Stock Exchange together will redefine global capital markets for decades to come," said Charles Li, chief executive of HKEX. "Both businesses have great brands, financial strength and proven growth track records. Together, we will connect East and West, be more diversified and we will be able to offer customers greater innovation, risk management and trading opportunities."

Per the FT, Li is trying to make HKEX into a "department store" for investors looking to increase their exposure to China just as Beijing is trying to open its markets to more foreign investment.