South Korea's telecommunications carriers turned on super-fast 5G mobile internet networks abruptly ahead of schedule in an attempt to ensure the country becomes the first in the world to launch the services.

The 5G networks of the three South Korean mobile operators went live at 11pm on Wednesday, hours before United States carrier Verizon turned on its 5G network in some areas of Minneapolis and Chicago a week ahead of schedule.

The carriers had initially planned to start their 5G services on Friday, but moved up to stay ahead of Verizon. The change came hours after a meeting between the carriers and government regulators, who modified service terms so that the companies could sign up users earlier.

However, the South Korean 5G services were initially available only to a few individuals selected as brand promoters, including figure skating superstar Yuna Kim, who SK Telecom announced as one of its "first customers". Regular customers in capital Seoul and some other major cities will be able to sign up for 5G services starting on Friday. The carriers plan to expand their coverage to 85 cities across the country by the end of the year.

“The government and private companies came together to achieve the world's first commercialised 5G services and this proves once again our country is undoubtedly the top powerhouse in information and communications,” said You Young-min, South Korean minister for science and information technology.

The supposed milestone is widely seen as symbolic. Park Tae-wan, a ministry official, said a “world's first” reference could possibly help the mobile industry market's know-how.

The carriers say 5G-enabled smartphones are capable of downloading data 20 times faster than existing 4G devices, which in theory would enable users to download movie files almost instantly. The faster networks would also improve live broadcasts and streaming services for music and video while allowing for a broader range of virtual reality services, the companies say.