HSBC has unexpectedly parted ways with its chief executive, John Flint, less than 18 months after his appointment and said it could cut nearly 5,000 jobs due to a weaker outlook.

The bank, which has its headquarters in the UK, was vague over the cause of Flint’s departure, saying only that the decision was “mutual” and that its board believed a change was needed to meet the challenges it faced.

It sparked a flurry of speculation over the cause of his exit, including whether he clashed with chairman, Mark Tucker, who was hired from outside the bank, or whether Flint – who was paid £4.6m last year – was pushed out amid political pressure from Beijing.

Chinese authorities were reportedly upset to learn that HSBC passed information detailing its relationship with the tech giant Huawei to the US Department of Justice in 2017. The request for information came while HSBC was being monitored by US authorities over sanctions-busting and a failure to prevent money laundering in Mexico. The information ultimately helped the US build a case that led to the arrest last year of Meng Wanzhou, Huawei’s finance chief and the daughter of its founder.

However, Tucker denied there had been any pressure from China over the Huawei episode that led to Flint leaving the bank.

Tucker added: “There’s been no personality clash, there has been no disagreement over strategy. This is a unanimous decision of the HSBC non-executives, so personalities have not been a factor in this at all.”

He also denied that Flint was opposed to new cost-cutting plans, which HSBC revealed on Monday would result in up to 4,700 job cuts, or 2% of its 237,685-strong global workforce. The move is expected to hit senior staff the hardest, helping to reduce salary costs by as much as 4%.

Flint, who could be entitled to a payoff of up to 12 months’ salary of £1m plus payouts for other bonuses and incentive schemes, was an HSBC stalwart and spent his entire career at the bank. But after 30 years’ service he is now the shortest-serving chief executive since the bank brought in its current governance structure in the mid-1980s. Shares in the bank fell 3% after Flint’s departure was announced, and are down 16% in his time as chief executive.

His ousting also marks a U-turn for the current board, including Tucker, who led the process of finding a success for the former chief executive Stuart Gulliver. Tucker joined the bank from the Asian insurance group AIA in September 2017.

“We made the best decision at the time … but there’s a belief that the environment we’re going into needs a different person to take that forward,” Tucker said. While he refused to explain why Flint was the wrong man for the job, he was quick to heap praise on his temporary replacement.

HSBC confirmed on Monday that Noel Quinn, the 57-year-old head of HSBC’s global commercial bank, will take over as interim chief executive. “We think Noel … brings pace, he brings decisiveness, he brings ambition, all of these things are important in the next stage and we feel he’s the right man for this time,” Tucker said.

While the bank says it is considering both internal and external candidates, Tucker’s comments have prompted speculation that Quinn could be a top candidate.

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John Cronin, a financials analyst at stockbroker Goodbody, said: “Based on his comments on the call, it would seem Noel Quinn is a serious contender for the seat on a permanent basis – and we would argue that, for a business as complex and challenging as HSBC is, it is probably sensible to stick with an insider (despite the Flint experience) in this environment.”

News of Flint’s departure was released alongside a strong set of half-year results, showing HSBC made pretax profits of $12.4bn (£10.2bn), up 16% year on year. However, the bank warned of a weaker outlook after the recent cut to US interest rates, simmering geopolitical issues and greater uncertainty around the Brexit outcome.

The poor forecast prompted HSBC’s cost-cutting plans, which it said would result in a one-off severance bill worth $700m for the full year.