After President Hosni Mubarak announced Tuesday he would not run for a new term in September elections but rejected protesters' demands he step down immediately and leave the country, clashes erupted between protesters and government supporters in the Mediterranean city of Alexandria and gunshots were heard, according to footage by Al-Jazeera television. More than a quarter-million people flooded into the heart of Cairo Tuesday, filling the city's main square in by far the largest demonstration in a week of unceasing demands for President Hosni Mubarak to leave after nearly 30 years in power.