South Korea launched the world's first nationwide 5G mobile networks two days early, its top mobile carriers said today, in a late-night scramble to be the first providers of the super-fast wireless technology.

Three top telecom providers -- SK Telecom, KT, and LG Uplus -- began their 5G services at 11 pm local time Wednesday, despite previously announcing the launch date would be April 5.

Hyper-wired South Korea has long had a reputation for technical prowess, and Seoul had made the 5G rollout a priority as it seeks to stimulate stuttering economic growth.

But speculation that US mobile carrier Verizon might start its 5G services early forced South Korean providers to hastily organise a late-night launch, Yonhap news agency reported.

In the event, Verizon began rolling out its 5G services in Chicago and Minneapolis on Wednesday US time, a week ahead of schedule.

But according to Yonhap, the South Korean launches came two hours earlier.

"SK Telecom today announced that it has activated 5G services for six celebrities representing Korea as of 11 pm April 3, 2019," the country's biggest mobile operator said in a news release Thursday.

The celebrities -- including two members of K-pop band EXO and Olympic ice-skating hero Kim Yu-na -- were "the world's first 5G smartphone subscribers", it said.

Both KT and LG Uplus said they also went live at the same time.

For general customers, the services will be available from Friday -- the previous launch date -- when Samsung Electronics rolls out the Galaxy S10 5G, the world's first available smartphone using the technology.

Verizon's system will work with Lenovo's Moto Z3 smartphone, while rival US carrier AT&T deployed what it called its 5G E network in 12 cities last year -- although it is slower than other 5G systems and questions have been raised over whether it is fully fifth-generation.

Experts say 5G will bring smartphones near-instantaneous connectivity -- 20 times faster than 4G -- allowing users to download entire movies in less than a second.

The technology is crucial for the future development of devices such as self-driving vehicles and is expected to bring about $565 billion in global economic benefits by 2034, according to the London-based Global System for Mobile Communications, an industry alliance.