CAIRO, April 2 (Reuters) - Some 500 Egyptian students broke into the headquarters of the country's top Islamic university on Tuesday to demand the resignation of its president following a mass food poisoning on campus, a security official said.

Around 460 Al-Azhar University students were hospitalised on Monday after eating at a cafeteria on campus, according to the Health Ministry. Most of the students were discharged on Tuesday morning.

Students said the incident was a sign of neglect by the president of Al-Azhar, a thousand-year-old mosque and university that draws students from across the Sunni world.

Some 500 students broke into the headquarters of Grand Sheikh Ahmed al-Tayeb, the top religious leader of Al-Azhar, to demand the resignation of university president Osama Al-Abd.

The university issued a statement on Tuesday warning students not to "exploit" the mass food poisoning, saying that such incidents have occured at other universities.

Protests on issues ranging from national politics to local grievances have become far more common in Egypt since the overthrow two years ago of autocratic president Hosni Mubarak.

The statement said that an initial investigation by the toxicology unit of Ain Shams hospital in Cairo revealed that contanimated food was responsible for the mass food poisoning.

President Mohamed Mursi visited some of the ill students at a hospital in the Cairo suburb of Nasr City on Tuesday morning.

A statement from the presidency said that Mursi, an Islamist, was "personally following" the students' health.

A senior official from the Freedom and Justice Party, the political wing of the Muslim Brotherhood, echoed the demands of the university students.

Essam El-Erian said the university's leadership was responsible for "disasters" like Monday's incident.

Egypt's prosecutor ordered an investigation into the incident on Tuesday. (Reporting by Maggie Fick)