Gas masks and hard hats at Hong Kong's protest pop-up store

Lee Ching-hei runs a pop-up store in Hong Kong but instead of offering the latest food trends or fashion must-haves he sells another highly sought-after commodity: protest supplies.

Helmets, goggles and gas masks are bestsellers at "National Calamity Hardware", which has held two pop-up sessions in the districts of Mong Kok and Tai Po -- both major hotspots during Hong Kong's two months of huge, sometimes violent, pro-democracy protests.

"We sold 50-60 sets of gas masks in the first hour of business, so we're sold out now," the 33-year-old businessman said while fitting a customer for a helmet ahead of a planned protest in Hong Kong's Tai Po neighbourhood. Lee said he had been an avid collector of gas masks -- dubbed pig snouts in Cantonese -- even before the protests began.

"So I had a really large number of 3M masks saved up," he said, referring to the most popular brand among protesters as his shop bustled with customers.

Hong Kong's protesters have been gearing up with increasingly protective equipment as clashes become more violent.

While millions have hit the streets for peaceful rallies, a minority of hardcore demonstrators have used bricks, Molotov cocktails and slingshots after police began routinely using tear gas and rubber bullets to disperse crowds.

The demonstrations started as rallies against a controversial bill that would allow extraditions to mainland China, but have since morphed into a call for greater democratic reform in the semi-autonomous city.

Now in their 10th week, the protests have seen violence escalate on both sides.

Earlier this week, Hong Kong police fired tear gas inside enclosed subway stations and rubber bullets at close range as colleagues baton-charged protesters down some station escalators.

One woman suffered a horrendous eye wound last weekend -- something demonstrators have blamed on a bean-bag round -- and dozens have been hospitalised with serious injuries.

The police have also reported casualties. In clashes last weekend, an officer sustained burns to his legs from a Molotov cocktail.

Lee said he sells supplies at a big discount to students, nearly 90 percent off, portraying his involvement as both a business opportunity and also a way to help young people.