Cairo: Three Vietnamese tourists and an Egyptian guide have been killed and at least 10 others injured when a roadside bomb blast hit their tour bus less than four kilometres from Egypt's world-famous Giza pyramids.

The bombing is the first deadly attack against foreign tourists in Egypt for over a year and comes as the tourism sector, a vital source of foreign currency revenue, recovers from a sharp drop in visitor numbers since the country's 2011 uprising.

The tourist bus after a roadside bomb near the Giza pyramids. Credit:AP

No immediate claim of responsibility was reported.

Islamist extremists, including militants linked to Islamic State, are active in Egypt and have targeted foreign visitors in the past.