South Sinai governor Khaled Fouda said the blast likely resulted from an explosive device planted on the bus, but he cautioned that an investigation has not been completed.
The bus was hit in the Taba area and it was the first attack on civilians in the restive area where terrorist attacks have been on the wane in recent months.
Egyptian security sources told Ahram Online the victims were Korean. Another 27 people of varying nationalities were injured.
Authorities have closed off the road leading to Taba to search for the perpetrators.
It is not clear why the bus was targeted.
Sinai experienced a surge in terrorist violence after last year's ouster of President Mohamed Morsi by the Egyptian military. The attacks, however, were generally aimed at military and police installations.
The Islamist group Ansar Beit al-Maqdis, which Ahram said had ties to al-Qaida, is based in Sinai and claimed responsibility for several attacks around Egypt.