To launch a double-chocolate Oreo flavor in China, Mondelez tapped two popular singers to ham it up in a live stream. One star, Da Zhangwei, had cookies shoved into his mouth while he sang Oreo's ingredient list to the tune of a love song. Fans were asked whether the other singer, Xue Zhiqian, should eat an Oreo smothered with fermented bean curd and wasabi. They voted no; he did it anyway.

The blend of celebrity and goofy antics hit the sweet spot: The show got 4.5 million unique live views when it aired early this month on four Alibaba platforms, according to Dentsu's Carat, which was behind the campaign.

Live streaming has exploded in China in the past year; in 2015, it was a $1.8 billion industry, according to Huachuang Securities, which predicted it could expand to $15.9 billion by 2020. And more advertisers are trying it, including P&G, Adidas and Sony. Marketers' efforts range from straightforward (store tours, product demonstrations) to bizarre, elaborate pieces of performance art. Condom brand Durex promised a live show with 50 couples in bed; they performed calisthenics and snacked on bananas, but there was no actual hanky panky, which annoyed viewers.

Some campaigns, like the effort from Oreo and Carat, tap directly into the mania for online shopping in China, the world's biggest e-commerce market and the biggest internet market, with 710 million people online. Over the past three weeks, Carat says, 26 million people watched the Oreo video on Alibaba's Tmall marketplace.

The buddy humor was designed to promote Oreo's playful brand image and its new flavor, called Double Enjoyment. People could click a buy button on their mobile screen to drop the Oreos into their shopping cart. The live broadcast set a sales record for Oreo on Tmall, the agency said, without divulging specific numbers.

Money and human connections

Live streaming is at the intersection of a few Chinese trends. "Young Chinese consume a lot of video compared to the U.S.," says R.K. Mani, managing director for international clients at Carat China. Plus, "it's live, it's interactive, it's reality content, which is very popular in China. And so it's really catching people's attention."

Streamers are generally ordinary people, telling stories or singing or showing scenes from their lives; attractive young women abound, dancing or acting coquettish.

Advertising on the platforms is still in the early stages, and the industry is monetized mostly with virtual gifts from viewers to online hosts. Using mobile payments, people can send virtual flowers -- even virtual yachts -- to their favorite hosts. That gets transformed into real money, and the platforms take a cut.

The exchange of money is driving interest. But there may also be social factors behind why live streaming really caught on here. China has a huge population of migrant workers living far from home, says Amber Liu, CEO of local agency Amber Communications. They're searching for connections online, as are young people who grew up as only children under the one-child policy. Live streaming is "a new and very important form of human connection," said Mr. Liu, whose agency has done live streaming work for Adidas.

China's platforms seem to get more interaction than Silicon Valley's; viewers' comments, and emojis, often stream right over the videos, and hosts react to gifts and comments in real time.

There are dozens of local live streaming sites including Huajiao, Bilibili, Ingkee and YY. Internet giants like Alibaba and Tencent have invested in the area.

A note of caution

China's government is keeping a close eye on live content; the Cyberspace Administration of China pushed for stricter rules on live streaming, including full-time monitoring. There have been penalties for hosts and platforms accused of broadcasting pornographic or violent content. In May, in perhaps the oddest internet regulation of all time, authorities even banned seductive banana-eating.

Durex's broadcast of 50 couples in April wasn't racy; it was just surreal. But soon afterward, without mentioning any brands by name, the anti-pornography office said on its microblog that it was concerned about vulgar marketing on webcast platforms and urged internet companies to "resist unhealthy content."

For most brands, crossing the line probably isn't a huge risk. And some in advertising argue that more regulated content might even make the live streaming space safer for brands.

But there are other factors that give some advertisers pause. They can't control users' comments, which are broadcast live and often stream across the screen in China, right on top of the image. That means any negative chatter will be front and center. "You have to be more cautious about what you are bringing to the brand," said Christina Liang, client general service manager for MediaCom in Beijing. "Since the nature of it is live, there's always more risk compared to other campaigns."

A few more examples of live-streaming campaigns in China:

-- To promote the ZX Flux shoe, which can be customized, Adidas live-streamed a graffiti artist doing a portrait of the sneaker. He changed his design and patterns according to the requests of people watching live via Bilibili. The campaign was from Amber Communications. (The agency's CEO says agencies should be working harder to find a strong brand connections in their live streaming campaigns; otherwise their efforts "can just seem like TV shopping channels," with somebody on a screen selling something.)

-- For a 4th of July event for American brands selling on Alibaba's Tmall platform, Macy's took Chinese consumers on a virtual tour of its 34th Street store in Manhattan. Macy's, which is closing 100 stores, partnered with Alibaba to test e-commerce in China starting last year.

-- China's Xiaomi showed off the battery life of its Mi Max phablet with a live stream on Bilibili that lasted 19 days, until the battery finally died. "It was touted as a 'boring live stream,' as technically, nothing much happened," a spokeswoman said. But the quirkiness drew viewers, and the brand says 39.5 million people checked it out.

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CORRECTION: A previous version of this story said Amber Communications, part of China's Leo Digital Network, did live-streaming work for Sony. An agency called Carnivo, also part of Leo, did the Sony work.