Two security sources said at least 17 people, mostly foreign tourists, were injured in the blast on Sunday.
South Africans and Egyptians were among those injured when an explosive device went off, hitting the bus, according to the sources.
There were no reports of deaths and the injuries were said to be of medium to minor degrees.
A witness, Mohamed el-Mandouh, told Reuters he heard a “very loud explosion” while sitting in traffic near the site of the blast.
Pictures posted on social media showed a bus with some of its windows blown out or shattered, and debris in the road next to a low wall with a hole in it.
The tourism industry is the only source of income for many people in the country.
Hospitality workers, tourist guides, coach and taxi drivers as well as many storekeepers and shops in the bazaars depend on tourists for their living.
The industry has been recovering since a sharp drop in the number of visitors after the turmoil of the Arab Spring in 2011 and the bombing of a Russian passenger jet in 2015, when 224 people were killed.
Russia plane crash in Egypt kills 224A Russian passenger aircraft carrying 224 people crashes in Egypt, killing everyone on board.
In December, three Vietnamese tourists and an Egyptian guide were killed and at least 10 others were injured when a roadside bomb hit their tour bus less than four kilometers from the Giza pyramids.