A competitor pours his brew in the finals of the Hong Kong Style Milk Tea contest held during the 2016 Hong Kong International Tea Fair. Tengku Bahar / Afp

Some cities are fueled by coffee. In Hong Kong, it's milk tea - a potent nostalgia-infused caffeine hit. And there's fierce competition to brew the best in town.

Thousands of restaurants offer the full gamut of international cuisines, but the city's no-frills diner-style restaurants, or cha chaan teng in Cantonese, some of them decades old, remain perennial favorites with locals and still do a roaring trade. They serve up cheap local dishes, from fried egg sandwiches and buttery French toast to noodle soups and macaroni.

The standard accompaniment is milk tea, or lai cha - a tangy, deep-tan brew made from blends of black tea strained repeatedly for strength, then mixed with condensed or evaporated milk.

The city gulps down around 2.5 million cups a day.

At Lan Fong Yuen, a family-run tea shop on a hilly market street in Hong Kong's Central district, business shows no sign of slowing after 60 years.

Owner Lam Chun-chung says the no-fuss nature of Hong Kong's tea restaurants plays a big role in their popularity in the fast-paced city.

"People are always in a rush. Having a quick bite with milk tea is fast and convenient," said Lam, who adds that his cafe has much more character than the growing number of sterile coffee shops.

"When you are here you feel a sense of community," he said.

Customers sit around shared wooden tables, many stopping for just 10 minutes to grab a quick breakfast or a midmorning boost.

A tea master juggles steaming pots on an electric stove, straining the hot brews through long cloth sieves, essential for any serious Hong Kong lai cha joint.

At this cafe, tea is strained seven times to intensify the flavor.

Milk tea has even made it onto an official list of the city's intangible cultural heritage. Hong Kong's Association of Coffee and Tea says it is also building a global fan base.

The association has been running Hong Kong milk tea contests worldwide for the seven years.

Earlier this month, competitors from Hong Kong, the Chinese mainland, Canada and Australia all competed for the Golden Cup award in the association's largest tea competition, on the home turf.

Local contestant Chen Chi-ping, 44, emerged victorious. He has been making milk tea in Hong Kong for 22 years.

"Every detail has to be strictly precise - the heat of the stove, the water temperature," he said.

Hong Kong-style milk tea has flowed through the city's arteries for more than half a century, according to association chairman Simon Wong, who tells how it was first served on Hong Kong's docks to sailors and laborers, an earthy adaptation of the weaker version made with fresh milk by the colonial British who governed at that time.

"Hong Kong people wanted something with more punch. So we invented this type of brewing," Wong says. The strength of the tea and the canned milk made it value for money - few ordinary Hong Kongers at that time could afford fresh milk.

The Chinese mainland has now also developed a taste for Hong Kong-style milk tea, and immigrant communities across the world are introducing it to new countries, Wong said.

The winning formula? Both tea champion Chen and cafe owner Lam agree: Passion.

"The most important thing is to put your heart into it," Chen said.