China is the largest country by total area with a single official time zone: China Standard Time, UTC+8.
China spans roughly 9.6 million square kilometres and stretches across about five geographic time zones. Nevertheless, the entire country officially follows Beijing Time. This means the clock can show the same official hour in far-eastern Heilongjiang and far-western Xinjiang, even though sunrise and sunset occur at very different local times.
China once used several regional time zones. After the establishment of the People’s Republic of China in 1949, the government standardized the country on Beijing Time. In Xinjiang, many residents and institutions also use an unofficial local time approximately two hours behind the national standard, but it is not a separate official national time zone.
India and Argentina also use one official time zone, while Algeria does too, but each is much smaller. Russia is larger than China by area, yet it officially spans eleven time zones, so it does not qualify.