Security sources who spoke on condition of anonymity told Reuters that at least four men threw crude fire bombs also known as Molotov cocktails at the cars, which were parked. State news agency MENA said the cars were parked in a lot in Suez's Arbaeen district.
Saudi Arabia has been a strong backer of Egypt since then-army chief Abdel Fattah al-Sisi toppled Mohamed Morsy of the Muslim Brotherhood last year and the attack appeared to be the first on Saudi property or personnel in Egypt since then.
Major General Tareq Butcher, director of security in the city, said authorities were working to identify the perpetrators of the attack.
The embassy of Saudi Arabia in Cairo declined to comment on the incident.
Tens of thousands of Brotherhood supporters are in jail as part of a security crackdown against the group on the Brotherhood since Morsy's ouster.
The Muslim Brotherhood says it is a peaceful movement but authorities accuse its members of being involved in a Sinai Peninsula-based Islamist insurgency that has killed hundreds of policemen and soldiers in the 15 months since Morsy's overthrow.
Top oil exporter Saudi Arabia and Gulf Arab allies United Arab Emirates and Kuwait have given Egypt billions in cash and petroleum products since Morsy's ouster.
