Nearly a million businesses in the UK and around the world can now set up a single online store to sell products, with no fee, on Facebook and Instagram.
The initial stage of the Facebook Shops rollout has been brought forward and extended because of Covid-19.
The stores will appear on business pages, Instagram profiles and through targeted ads.
The company has already used a no-fees approach in its Facebook Marketplace for personal classifieds.
"It's bigger than usual just because we want to make sure we're moving quickly to get these tools in the hands of as many businesses wherever they are, big or small, to help them survive during this time," Facebook's Layla Amjadi said.
And product manager George Lee said it had been in the pipeline for at least half a year.
"Obviously, given the current situation, we have accelerated a lot of our efforts," he said.
"We're in a unique position to be able to contribute to the survival of a bunch of these businesses."
The shopping feature will also eventually appear on WhatsApp and the company's other messaging apps and integrate with live streams.
For the average Facebook user, "this will be a really seamless experience," Ms Amjadi said.
"You can go much deeper now without having to leave the app."
Once a buyer decides they want to spend money, they will usually be directed to the company's website to complete the transaction.
And if problems arise or a buyer wants to ask questions, they can do so through Facebook Messenger, WhatsApp, or Instagram Direct messages, some of which are already used by companies for that purpose.
The rollout is part of a wider range of changes planned for shopping across Facebook's products, including:
- a loyalty scheme that will link things such as points from local coffee shops to Facebook
- a Shop button, where products and brands will be showcased, on Instagram's main navigation bar
Anthony Ha, a senior writer at technology news site TechCrunch, said the pandemic lockdown may have worked in Facebook's favour.
"After all, if your favourite store has changed their hours, or switched to online delivery or kerb-side pickup, they've almost certainly posted about it on Facebook or Instagram," he said.
"So it makes sense for Facebook to make the purchase process as easy as possible from those profiles.
"From a business perspective, the obvious goal is to drive more advertising.
"But it's also worth remembering that the pandemic's economic fallout will likely kill off many small business - including the ones that post and advertise on Facebook.
"So the company has a stake in helping those businesses survive in any way it can."