CAIRO, July 2 (Reuters) - Supporters and opponents of Egyptian Islamist President Mohamed Mursi exchanged gunfire in the city of Suez at the mouth of the Suez Canal on Monday, witnesses said.

At least 16 people have been killed in clashes between rival protesters since Sunday, when millions of Egyptians flooded the streets to demand Mursi resign.

"The sound of gunfire is everywhere. Supporters and opponents are going back and forth," said one witness, Karim el-Sayed, in Suez. (Reporting by Yusri Mohamed; Writing by Alexander Dziadosz; Editing by Kevin Liffey)