21st Century Fox (FOXA) has held talks to sell most of its assets to Walt Disney (DIS), a deal that would create a seismic shift in the media and entertainment industry, according to media reports.

Discussions between the corporate parents of the 20th Century Fox film studio and the Walt Disney World Resort have taken place over the past few weeks but aren't currently active, although they could be revisited given their "on again, off again" nature, CNBC's David Faber reported. The Wall Street Journal, however, offered a more pessimistic take, saying the talks were preliminary and had broken down over price and other issues. An analyst estimated the value of the deal between $20 billion and $30 billion.

"Disney hates to overpay for assets," said Laura Martin, an analyst with Needham & Co., who has a hold on Disney and Fox, in an interview, adding that it's a "great strategic idea." "When you merge two studios together, you create a tremendous amount of value. Disney has had a much better TV production unit than Fox."

Antitrust issues would complicate any transaction between two multi-national media conglomerates.

That's why Burbank, Calif.-based Disney would presumably want to acquire Fox's movie and TV production businesses along with entertainment networks such as National Geographic and FX, CNBC said. It wouldn't buy the Fox broadcast network, Fox Sports, the Fox News and Business channels or the company's local television affiliates.

Disney would have also acquired Fox's 39 percent stake in U.K. pay television operator Sky Plc, the Journal says. Fox's $15.5 billion offer to buy the part of Sky that it doesn't already own has been held up by U.K. regulators.

If Disney and Fox join forces, it would accelerate "the arms race" for content that has been jumpstarted by new rivals in the entertainment business such as Netflix (NFLX) which have siphoned off consumers from traditional media companies in recent years, according to Tuna Amobi, an analyst with CFRA.

"Investors have shifted in how they view the media landscape," said Amobi, who rates Disney as a "buy" and Fox as a "hold" in an interview. "With a lot of the shares underperforming, it just seems that the sector is in need of a major catalyst. A deal like this could provide that catalyst. … It's really telling that scale matters and it's going to matter even more."

Indeed, Martin argues that other media companies including Viacom are going to need to find merger partners to compete against Netflix and other new deep-pocketed rivals such as AT&T (T), which is in the process of acquiring Time Warner (TWX), the parent of Warner Bros. and CNN, and Amazon.com (AMZN).

Fox and Disney are co-owners of the Hulu streaming network, whose "Handmaid's Tale" won the Emmy award this year for Best Dramatic Series, along with Comcast (CMCSA) and Time Warner.

Shares of 21st Century Fox, which are controlled by the Murdoch family, rose $2.48, or 10 percent, to $27.48. Shares of Disney, which owns Marvel, Pixar among other entertainment brands, rose 2 percent to $100.64.

Officials from Fox and Disney couldn't immediately be reached.