Advisers to HSBC say the US is one of the few countries with an economy big enough to be able to comfortably welcome a bank of its size. HSBC has $2.6tn of assets, making it almost as big as the entire British economy. Bankers also view US financial regulation as more accommodating of large universal banks.
Douglas Flint, chairman of HSBC, told the Financial Times the bank was "about halfway through the process" of considering moving its domicile and had "prepared the ground by giving presentations to the board on the various aspects, like the regulatory and economic framework, but we have not had any discussion of the relative merits".
One top 10 shareholder in HSBC said: "I would say Hong Kong would be the best location as that is where HSBC have their history, but there is political risk in Hong Kong. The US has to be a serious option. You have a more friendly regulator in the way they look at bank capital and they have the balance sheet to take on HSBC. I think the US would love to have a bank like HSBC."
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Another top 10 shareholder in HSBC said: "I think longer term Hong Kong must be the favoured location, if the bank is going to move. But the US is definitely an option too, but I would have said it was the second option."
Advisers to HSBC said the Chinese government's interventionist reaction to volatility in its stock market this summer raised doubts about Hong Kong as a destination.
Yet Mr Flint denied this. "As every country reacts to unforeseen circumstances, they learn from what works and what doesn't. But that doesn't have a bearing at all on our decision," he said.
The advisers also said the bank's 20-strong board was worried about whether a possible move to Hong Kong would upset UK and US regulators, with potentially negative consequences for the bank.
Mr Flint said: "It is not rocket science that the views of regulators would be a subject we would think about. We would have to take that into account."
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The advisers said HSBC was concerned about the potential impact on its deferred prosecution agreement with the US Department of Justice, which it signed to avoid criminal charges over money laundering and sanctions violations in 2012.
One person familiar with the DoJ's thinking said it would not be happy about HSBC moving its headquarters to Hong Kong. Such a move could also put the bank's highly prized US dollar clearing licence in the balance, one adviser said.
However, several state-controlled Chinese banks already have US dollar clearing operations, including Bank of China, China Merchants Bank and China Construction Bank. Earlier this year, US regulators ordered China Construction Bank to overhaul its anti-money laundering programmes, including improving customer due diligence on dollar clearing activities.
HSBC plans to update investors early next month on its discussions and aims to decide by the end of the year with a vote by the full board, though Mr Flint said this may slip into 2016.