In high-rise, high-priced Hong Kong, even millionaires don't always have room to store their fine wine collection at home, but a converted British war bunker offers space-crunched oenophiles the perfect solution.

Built by Her Majesty's government in the 1930s to hold munitions, the "Little Hong Kong" bunker complex was the last Allied position to fall to the invading Japanese on 27 December 1941 -- two days after the surrender of the British governor.

Collectors may rest assured that this spirit endures, says Gregory De 'Eb company principal of Crown Wine Cellars.

"We have great feng shui here. Nobody died, last place to surrender -- it was all good!" he explains.

The firm has converted the sprawling complex into state of the art wine storage. Six of the Central Ordnance Munitions Depot bunkers -- each spanning some 1,000 square feet -- have been painstakingly transformed in to what he describes as "the Rolls Royce of wine cellars."

Carved out of Hong Kong's hills, protected by reinforced concrete and soil, the complex -- whose sensitive restoration even received a nod from UNESCO -- offers one of the most secure environments possible for wine.

"If you give us one bottle of 1982 Petrus that your grandfather gave to you (with) his signature on the top left hand corner, we make absolutely sure that your bottle will never be interchanged with any other," said De' Eb, a former diplomat.

"In 50 years time we will give that bottle back to you. It's so important," he added.

- 'Gold standard' security -

De' Eb says the wine vaults were built in accordance to the US standard for gold bullion, while overall security at the bunkers drew inspiration from methods employed by the diamond industry in his native South Africa.

Staff must wear wetsuits when entering the cellars -- an anti-theft measure to ensure nothing can be smuggled out in clothing, and some vaults require three people to simultaneously input codes in order to access them.

Clients are not allowed to enter the main storage warehouses, but can request to view their wine collection in small rooms, where they will be closely monitored by security cameras.

Such measures are not just for show: the cellar holds two of the world's most expensive bottles of wine ever sold at auction -- Chateau Lafite 1869 that went under the hammer in 2010 at Sotheby's Hong Kong, fetching 232,692 dollars (208,000 euros) apiece.

Thanks to Hong Kong's incredible concentrations of wealth, the city has become a world capital for fine wine.

The city hosts Vinexpo, Asia's largest wine and spirits fair, and has become a major hub for fine wine sales across Asia, thanks in part to a government decision in 2008 to drop import duties on wine.

Imports have grown exponentially -- to $1.5 billion in 2015, up from $206 million in 2007 according to Hong Kong Trade Development Council figures.

The city is a key gateway to the vast, lucrative Chinese market, but of the 63.3 million litres of wine that was imported into Hong Kong in 2015, just 27.2 million was re-exported -- highlighting the city's own love affair with grapes.

- Where to keep it? -

Astronomical real estate prices coupled with Hong Kong's hot and humid environment, mean that "wine storage really is a growing business," said Korean wine expert Jeannie Cho Lee.

"It's not like in France where everyone has a basement under their house," said wine importer Alex Yim.

"In Hong Kong, you even need to find a place to store your clothes," he added, referring to the city's notoriously small but expensive apartments, which often lack basic storage space.

The government has sought to encourage the nascent local wine storage industry, creating the world's first Wine Storage Management Systems Certification Scheme in 2009.

By the end of 2015, 37 Hong Kong companies had been certified, giving wine-lovers many options.

They could trust their entire collection to Crown, which has 2,000 customers including major auction houses like Sotheby's, and manages "more than three billion Hong Kong dollars," worth of wine, De' Eb said.

The company is an arm of Crown Worldwide, which also has relocation, record management and fine art divisions.

Or they could turn to companies like Wine Vault, which started in 2008 and has converted disused industrial space into individual climate-controlled wine storage rooms.

The firm's cellars are between 40 and 80 square feet in size, and users can access their wine collection whenever they want, thanks to facial recognition software.

The rooms off the long corridor in the bland industrial complex are now packed with cases and bottles of the world's best vintages: Petrus 1966, Chateau Margaux 1981, Graves 1928, Barolo 1945.

"In order to mimic the environment of underground cellars in Bordeaux or other wine regions we keep the temperature around... 13, 14 degrees," said Hubert Li, a partner at the Wine Vault.

"All of our 550 clients are private collectors," he said, adding that sometimes clients send their drivers to collect a few more bottles to top up their smaller wine fridge at home.