Nintendo's first Mario smartphone title has set a download record but gamers find the cost of unlocking content high.

Super Mario Run hit 25 million downloads just four days after its Dec. 15 release in 151 countries on Apple's App Store, earning gross sales of about $21 million, showed data from app analyst Sensor Tower.

But the game has received negative reviews from users mainly complaining about its $9.99 one-time cost, rather than the usual model of paying small amounts for special features.

Super Mario Run is free to download on the App Store where, in Japan, it is rated 2.5 stars out of 5 based on 1,095 reviews.

Nintendo decided to enter smartphone gaming after resisting initial pressure from shareholders concerned about that segment's threat to its core console gaming business.

Soon after, Pokemon GO reached 25 million downloads in a then-record 11 days from about 35 countries via the app stores of Apple and Alphabet 's Google.

Nintendo has also said profit was not the only focus of its smartphone business. The company hopes to maximize the number of people who interact with its game characters on mobile, to bridge them to console gaming and to create synergies.