Google is developing a version of its search engine that will conform to China's censorship laws, reports say.
The company shut down the engine in 2010, complaining that free speech was being limited.
But online news site The Intercept says Google has been working on a project code-named Dragonfly that will block terms like human rights and religion, a move sure to anger activists.
One state-owned newspaper in China, Securities Daily, dismissed the report.
When questioned about the claim, a spokeswoman for Google provided a brief statement.
"We provide a number of mobile apps in China, such as Google Translate and Files Go, help Chinese developers, and have made significant investments in Chinese companies like JD.com," it said.
"But we don't comment on speculation about future plans."
What has The Intercept said?
Citing internal Google documents and inside sources, it said that Dragonfly was begun back in the spring of 2017 and accelerated in December after Google's CEO Sundar Pichai met a Chinese government official.
It said an Android app with versions called Maotai and Longfei had been developed and could be launched within nine months if Chinese government approval was won.
Both Reuters and Agence France-Presse said separate sources had confirmed the report to the news agencies.
How would the engine work?
The search app would "blacklist sensitive queries", The Intercept says, identifying and filtering websites currently blocked by China's so-called Great Firewall.
According to documents it had seen, a search via the app would result in a list with banned websites removed and a disclaimer saying that "some results may have been removed due to statutory requirements".
It said the BBC News website and Wikipedia would be among those blocked.
What has been the reaction inside Google?
Google has not officially commented on The Intercept report.
Spokesman Taj Meadows told AFP: "We don't comment on speculation about future plans."
One worker who spoke to Reuters said he had transferred himself out of his unit to avoid being involved in the project.
Another source who spoke to AFP said: "There's a lot of angst internally. Some people are very mad we're doing it."
But some believe such a move should not be a surprise.
Chief executive Sundar Pichai was quite clear about his ambitions when he told a conference in 2016: "Google is for everyone - we want to be in China serving Chinese users."
And from activists?
Amnesty International said Google should not proceed with the programme.
Patrick Poon, a China researcher for Amnesty, said in a statement: "It will be a dark day for internet freedom if Google has acquiesced to China's extreme censorship rules to gain market access.
"In putting profits before human rights, Google would be setting a chilling precedent and handing the Chinese government a victory."
What has China said?
Not a great deal. However, the state-owned Securities Daily cited "relevant departments" as saying reports of the return of Google to the Chinese market were not true.
Reuters quoted a Chinese official as saying that Google had been in contact with Chinese authorities on the matter, but there was no approval for the programme as yet.
Why would Google want back in?
Quite simply, China is the biggest internet market in the world.
Despite its main search engine and YouTube video platform being blocked, Google still has more than 700 employees and three offices in China, and has been developing alternative projects.
Its Google Translate app for smartphones was approved in China last year.
It also invested in Chinese live-stream game platform Chushou in January and has launched an artificial intelligence game on the social media app WeChat.
What does China block?
There's strict censorship of popular Western sites, including Facebook, Twitter and Instagram.
Certain topics like the Tiananmen Square protests in 1989 are completely blocked. References to political opposition, dissidents and anti-communist activity are also banned as are those of free speech and sex.
China has in the past two years imposed increasingly strict rules on foreign companies, including new censorship restrictions.
Prize greater than principles?
Analysis by Rory Cellan-Jones, Technology correspondent
"Don't be evil" may no longer be Google's motto, but most of its employees still see themselves as working for a business that puts long-term principles ahead of short-term profit.
One of those principles is freedom of expression, so if it does go ahead with a censored search engine for China it can expect plenty of pushback, not only from civil liberties groups but from its own staff.
After all they managed to end a deal with the US military over software for targeting drone strikes.
This time the prize - access to the vast and growing Chinese market - is much bigger.
But Google is already being warned that complying with Chinese censorship is a complex business requiring an army of moderators.
It may decide that the damage to its brand in the West is too high a price to pay for a venture into China whose success is far from guaranteed.