Australian bike retailers are struggling to keep up with the boom in sales since coronavirus restrictions came into force last month.

“We’re the new toilet paper and everyone wants a piece,” Grant Kaplan, manager of Giant Sydney, a bike store in Sydney’s CBD, tells Guardian Australia.

“We can’t keep up with sales. Literally the phone is ringing nonstop,” he laughs, as another call came through in the background.

At first, casual employees, such as Giant Sydney’s Sean Marshall, were worried the Covid-19 restrictions would see them out of work.

But within a week of the state lockdown, Kaplan was offering his casuals extra shifts, saying if anything they were “short-staffed given the upturn in bike sales”.

The store has had to stop servicing bikes – typically a major source of revenue – because its mechanics are overrun with putting together customers’ new purchases.

Marshall, who has worked in bike sales for the last four years, tells Guardian Australia he would expect to see $10,000 in sales on a Saturday, but for the past two weekends “have done $40,000 each Saturday, with similar sorts of levels during the week as well”.

South Melbourne’s bikeNOW is seeing similar figures. Co-manager Nathan Ziino says they sold between 40 and 45 bikes last weekend, many of which are entry-level models costing $700 to $1,200.

No one wants to be stuck on a tram in winter during flu season, especially with coronavirus Nathan Ziino

bikeNOW typically sells $4,000-$15,000 bikes to high-end clientele. But Ziino says most of the shop’s recent customers have been families wanting to stay active while social distancing.

“Families are sick of walking everywhere as their form of exercise. The kids are home from school or being home-schooled. If you go to a football oval and there are lots of people already there, you can’t go on [due to social distancing measures],” he says.

“But on your bike you are exercising and practicing social distancing.”

For others, coronavirus restrictions have finally given them the time to take up a new hobby.

At Giant Sydney, Marshall says many customers have told him they long wanted to take up bike riding, but didn’t have the time or motivation before now.

“They talk as though they have been thinking about it, and now the ideal scenario has come up: they have the time of their hands, gyms are shut, pools are shut, so why not get a bike?”

Ziino predicts they will see a second rush of customers once social distancing measures are eased, consisting of those who have to start commuting to work again but don’t want to risk catching public transport.

“No one wants to be stuck on a tram in winter during flu season, especially with coronavirus,” he says.

Public transport usage in Sydney fell by about 75% in March, Transport for New South Wales reported, with the fewest number of people using the city’s rail, bus and ferry network in almost a century.

Bicycle Network – Australia’s peak representative body for cyclists – has called on governments to transform roads into cycleways to ease traffic on bike paths, as has already happened in parts of Germany and California.

A two-hour count of shared paths in Melbourne found the number of riders had increased up to 79% in some areas, Bicycle Network reported.

Meanwhile, experienced riders have bought out Australia’s supply of digital “bike trainers” – devices that allow cyclists to hook up their bikes to their computers and ride through virtual tracks from the comfort of home.

Ziino says bikeNOW sold out of bike trainers within two weeks of the lockdown, speculating that many regular riders “can no longer put a bike in their car, park near a trail and ride, because police will pull them over and fine them if they are far from home”.

The trend in digital bike riding is not unique to Australia: the 104th edition of the Tour of Flanders bicycle race through Belgium two weeks ago was forced to go online, with 13 professional cyclists riding the 32km race from home using these trainers and the virtual reality app, Zwift.

Marshall was one of the thousands of fans who logged on to YouTube to watch the riders’ digital avatars racing through a virtual landscape, spliced with webcam shots of their real-life counterparts peddling away in their living rooms.

The biggest problem facing retailers, Kaplan says, is that they will soon run out of stock.

Many of the bikes Sydney’s Giant Bikes sell are made in Taiwan and China, where factories have stopped production for some time due to the country’s coronavirus lockdown.

“It’s kind of a double-edged sword: overdemand and lack of supply,” he says.