Kiribati is widely described as the first country to welcome the New Year because its Line Islands use UTC+14.
Kiribati is an island country in the central Pacific Ocean. Its eastern Line Islands, including Kiritimati, lie on the world's most advanced standard time zone, UTC+14. As a result, midnight arrives there before it reaches most other inhabited places when dates are compared internationally.
The situation changed in 1995, when Kiribati moved the International Date Line around its eastern islands so that the country's territory would share the same calendar date. Before that change, the country was divided by the date line and some islands were nearly a day apart on the calendar.
“First country” is a convenient description, but the precise claim concerns the country's eastern islands and their time zone. New Zealand, Fiji, and Tonga also welcome the new year early, but their standard time zones are behind UTC+14.