From his office at the top of a 68- storey skyscraper he owns in Hong Kong's financial district, one of Asia's richest men would have been watching anxiously the "live" vote- counting in Britain.
Mr Li Ka Shing's assets in Britain include a telecoms operator, a pharmacy chain, three ports and a string of gas, water and electricity firms. In all, they account for over a third - or HK$23 billion (S$4 billion) - of his flagship CK Hutchison's earnings before interest and taxes last year .
A Brexit, or British exit, from the European Union means those billions are at stake.
"With the pound dropping 7 to 8 per cent, the currency loss will erode the earnings of firms with investments in the UK," says OCBC Bank economist Tommy Xie.
Investors agreed. CK Hutchison's shares dropped 6.3 per cent yesterday - leading the 4.8 per cent plunge in Hong Kong's Hang Seng Index.
As the vote counts came in, nailbitingly bit by bit yesterday morning in Asia, major markets in the region were the first to react. All tumbled - among them, Japan's Nikkei plummeted 7.92 per cent, its worst rout since March 2011, as investors calculated how badly Asian economies would be affected.
The most immediate impact is on companies with operations in Britain. Beyond that, they will have to rethink their business strategy of using the country as a gateway to Europe, say analysts.
Besides Mr Li, other big players include India's billionaire Ratan Tata, who owns Jaguar Land Rover and Tata Steel, Japan's car giants Toyota and Nissan, and China's Mr Wang Jianlin who owns Sunseeker yachts.
Smaller enterprises, too, will be affected. India alone has 800 firms with operations in Britain.
As the companies regrouped after the shock, some put forward a brave front. A CK Hutchison spokesman said: "We are confident that our UK businesses - which are strongly focused on providing vital goods and services to UK communities - will continue to thrive."
India's National Association of Software and Services Companies said there will be a "phase of uncertainty in the near term" but added there could also be opportunities for non-EU skilled workers.
For now, anxiety is permeating Asia. With the region accounting for a quarter of Britain's top 25 trade partners, Asia's prime ministers, finance ministers and central bank chiefs all quickly stepped out to assuage concerns.
In Japan, which analysts say is shaping up to be a prominent casualty, Finance Minister Taro Aso said it will respond to "extremely nervous" exchange rate moves. The yen surged to a two-year high, which could damage economic recovery and hurt exports.
"I'll closely watch currency market moves more than ever with a sense of urgency and will respond firmly when necessary," he added.
Bank of Japan governor Haruhiko Kuroda said the central bank was ready to pump liquidity into financial markets, though his deputy declined to confirm if monetary easing was on the cards.
In Hong Kong, the turmoil in the equity market means the chances of a recession - already looming - is higher, says Mr Xie. Financial Secretary John Tsang said the city has set aside sufficient liquidity.
More broadly, the risk is over whether more European countries will follow the path of Britain, says DBS economist Irvin Seah.
"It'll be a messy affair and the impact on the global economy, including Singapore, will be severe. This is negative for the global economy, which is still struggling with the structural slowdown in China. It'll be a double whammy for emerging Asia."
One key question now is what will happen to existing trade deals or negotiations. China, for one, is in a quandary. The EU was its largest trading partner last year, with two- way trade totalling US$564.9 billion (S$762.1 billion), according to Customs data.
With Britain's exit, China loses an ally in the EU. China is hoping to negotiate a free trade agreement (FTA) with the EU, which outgoing British Prime Minister David Cameron had earlier pledged to facilitate.
The Japan-EU Economic Partnership Agreement, for which talks have been ongoing since 2013, could also be in jeopardy.
Looking ahead, Britain will have its work cut out, trying to hammer out new deals with the region. Advocates of Brexit have said it could turn to Commonwealth countries.
But HDFC Bank economist Shivom Chakravartis warned it would not be feasible to assume that Commonwealth countries could replace the EU as a market for Britain.
South Korea's Foreign Minister Yun Byung Se said it would consider an FTA with Britain.
Mr Duncan Innes-Ker, regional director for Asia at the Economist Intelligence Unit, also sounded a note of optimism. It remains unclear exactly what the terms of Britain's future relationship with the EU will be - there are even scenarios under which it could remain within the bloc, he noted.
But, he added: "The biggest takeaway for now is that we are entering a period of uncertainty that will last for several years. That will be extremely damaging for business investment in the UK, from Japan and more generally." •Additional reporting by Chang May Choon, Grace Leong, Joyce Lim, Nirmala Ganapathy, Teo Cheng Wee and Walter Sim.