As the bus route goes through the centre of Kowloon Peninsula, buses on this route are usually full, with the route serving as one of Kowloon's major bus routes.
The route was started in the 1920s, then known as Route 6. The route served between Tsim Sha Tsui and Kowloon City. Fares were divided into first and second classes at that time.
The route ceased operation during the Battle of Hong Kong in December 1941 and resumed January 10, 1942 as the Japanese military government in Hong Kong reorganized the bus services.
The route was renumbered Route 1 in October, 1942.
August 12, 1943, the route was shortened to serve between Tsim Sha Tsui and Waterloo Road due to shortage of fuel.
During the final days of Japanese occupation, this route was the only bus route remaining in service in Kowloon.
In mid-February, 1946 KMB resumed the route.
The first four double decker buses in Hong Kong were allocated to this route on April 17, 1949 as the population in Yau Ma Tei, Mong Kok and Kowloon City increased rapidly.
The route was one of only few routes still in service in Kowloon during the 1967 riots.
In 1972 the route was extended to Wang Tau Hom to serve newly developed areas.
In 1976 the route was extended to Lok Fu to serve newly developed areas.
In 1984 the route was further extended to Chuk Yuen Estate, its current terminus.
Single decker buses were used before World War II, and double deckers joined the route from 1949. Air conditioned services started from 3 August 1992, and since 2014, more Volvo B9TL buses have been deployed in the route. However, the B9TLs have been replaced by 15 Enviro500 MMCs operating this route.