Playfish's entire China-based team is working on a version of Electronic Arts' super-popular SimCity franchise for Facebook.

It will go toe-to-toe with Zynga's CityVille, the most popular game on Facebook that has held its spot for more than a year, according to AppData.

Multiple sources told that SimCity has been in development for more than a year. Electronic Arts started working on SimCity for Facebook around the time CityVille was in development.

When CityVille came out and quickly became the most popular game on Facebook, Electronic Arts had no choice but to "develop the hell out of SimCity" to make sure it was on par with Zynga's city-building game, one source told us. Electronic Arts told the Playfish team in China to drop other games in development and work on SimCity.

Zynga had more time and resources to invest in CityVille than Electronic Arts did into SimCity, sources said. It had a huge marketing budget and a team of more than 100 people working on it. One source said EA's priority was to make a social version of The Sims and it had "doubled down" on development and marketing for The Sims Social.

Playfish's Norway- and San Francisco-based teams are working on social games that are completely new pieces of intellectual property for Electronic Arts.