HSBC Holdings plc (HSBC) shares gave back earlier gains Monday, but modestly out-performed the broader market, after it posted stronger-than-expected first half earnings and announced the surprise departure of CEO John Flint less than two years at the head of Europe's biggest bank.

HSBC said pre-tax profits for the six months ending in June rose nearly 16% from the same period last year to $12.41 billion, thanks in part to a boost in retail banking revenues in Asia, where the London-listed group earnings more than 80% of its profits. HSBC cautioned, however, that lower global interest rates, rising U.S.-China trade tensions and the uncertainty surrounding Britain's exit from the European Union could weigh on sentiment -- and its broader bottom line -- over the second half of the year.

The larger news, however, was the surprise departure of Flint, the 51-year-old HSBC veteran who was tapped to replace Stuart Gulliver as group CEO in February of last year. Chairman Mark Tucker said the move was needed to order to accelerate the bank's turnaround strategy, which will continue to focus on Asia growth and the under-performance of its U.S. businesses. 

"It has been a privilege to spend my entire career with HSBC, rising from International Officer Trainee to serve as Group Chief Executive. I am grateful to my wonderful colleagues at the Bank for their support during my career, and I am proud of what we achieved together," Flint said in a statement Monday.

"I have agreed with the Board that today's good interim results indicate that this is the right time for change, both for me and the Bank," he added.. "After almost 30 years with HSBC, I will be sad to leave but I do so looking forward to a new personal challenge, and confident that our people will continue to serve the Bank's stakeholders in the best possible way."

HSBC shares were marked 2% lower in the opening minutes of trading in London, compared to a 2.17% decline for the broader FTSE 100, and changing hands at 632.9 pence each.

HSBC also confirmed multiple media reports, first published by the Wall Street Journal, that it will slash its global workforce by around 4,000 people in move that will cost between $650 million and $700 million in severance payments.

"It's about 4% of our total salary costs, so you should assume from that it is targeted at more senior people in the organization," CFO Ewen Stevenson told investors on a conference call Monday.