The popular video-sharing platform, which has around one billion monthly users, has faced restrictions in many countries for allegedly breaking data rules and for its potential harmful impact on youth.
"The decision to ban was made today, and relevant authorities are currently addressing the technical issues," Minister for Communications and Information Technology Rekha Sharma said.
Sharma said the decision was made because TikTok was consistently used to share content that "disturbs social harmony and disrupts family structures and social relations".
She did not specify what had triggered the ban.
Hours after the decision was made public, videos on the ban had thousands on views on TikTok.
Gagan Thapa, leader of the Nepali Congress party which is part of the ruling coalition, said the government's intention seems to be to "stifle freedom of expression".
"Regulation is necessary to discourage those who abuse social media, but shutting down social media in the name of regulation is completely wrong," he said in a post on X, formerly known as Twitter.
The decision comes days after Nepal introduced a directive requiring social media platforms operating in the country to set up offices.
TikTok is the sixth most used social platform in the world, according to the We Are Social marketing agency.
Multiple countries have sought to tighten controls on social media due to their potential impact on children.
TikTok's owner, ByteDance, is Chinese, but the company rejects critics who accuse it of being under Beijing's direct control.
Although it lags behind the likes of Meta's long-dominant trio of Facebook, WhatsApp and Instagram, its growth among young people far outstrips its competitors.