Service was resumed on 1946-04-16 between Central Ferry Piers and Queen Mary Hospital, with initially only two buses running and a frequency of one hour per bus, to be increased gradually. On 1968-10-03 the route was further extended to Wah Fu Estate with the completion of the estate's first phase. Since transportation was inconvenient for the estate, route 4 became the major means of transportation for the residents. As the population of Wah Fu increased, an express service was implemented in 1971, which faced delays caused congestion problems along Des Voeux Road West. On 1972-05-01 the express service was rerouted to serve Caine Road and Bonham Road in Mid-levels to bypass the congestion, seeing full daytime service and becoming a normal route, denoted by red text on yellow background. On 1975-01-01 the express service was renumbered 40.
On 1972-09-11 the Central terminus moved to a bus terminus opposite to Hang Seng Bank headquarters, on 1994-12-05 to Harbourview Street, and on 1995-03-17 to the new ferry piers. On 1998-09-01 the route was taken over by New World First Bus as part of the franchise handover. Air-conditioning of the route started on 1999-07-11 and completed in 2000.
The route has seen a drop of patronage since the 1990s with Citybus taking over some of the Wah Fu routes and having lower fares than route 4. On 2004-12-19 the route became a circular route, and ceased to serve Hong Kong Station and the ferry piers.