Egypt declared a state of high alert Saturday as police clashed with protesters who raided a building housing the Israeli embassy in Cairo, prompting Washington to call for protection of the mission.

Hundreds of Egyptian soldiers backed by armoured cars were rushed to the embassy district after US President President Barack Obama called on Egypt to protect the Israeli embassy.

During the violence, in which one person died of a heart attack and 448 people were injured according to state television, protesters torched police trucks and attacked regional police headquarters nearby.

Earlier protesters dumped thousands of Israeli embassy documents from the building housing the mission after they took down its flag and threw it to the crowd.

Egypt's Interior Minister Mansur al-Eissawy declared a state of high alert and the government announced it was convening an emergency meeting to deal with the crisis.

Early Saturday, Israel's ambassador flew out of the country, heading back to Israel, sources at Cairo airport told AFP.

Egyptian state television reported that ambassador Yitzhak Levanon met with a general of the ruling military's Supreme Council of the Armed Forces before his departure, and that the ambassador appeared "anxious and even scared."

Levanon had only recently come back to Cairo from vacation in Israel as protests raged outside the embassy since last month.

Obama on Friday made his call as he spoke by telephone to Israeli Prime Minister Benjamin Netanyahu, the White House said in a statement.

"The president expressed his great concern about the situation at the embassy, and the security of the Israelis serving there," it said.

Israeli Defence Minister Ehud Barak called US Defense Secretary Leon Panetta early Saturday to request help protecting their embassy in Cairo, a statement from his office said.

Hours after the violence broke out, Egyptian soldiers backed by armoured personel carriers massed near the embassy as power was cut to street lights in several blocks around the mission.

Protesters were still playing cat-and-mouse with police throughout the night, amid clouds of tear gas and smoke from burning tyres.

Thousands outside the embassy had jostled to grab the documents fluttering down from one of the top floors of the highrise where the embassy is located.

The documents, in Arabic, English and Hebrew, bore the watermarks of the embassy. They ranged from requests to Egyptian authorities for weapons permits for embassy security to internal correspondence on vacations.

State television quoted an interior ministry official as saying that "foreign hands" were behind the violence. Egypt's rulers often blame foreigners for unrest in the country.

Earlier Friday, thousands of protesters had massed in Tahrir Square to demand reforms and an end to military trials of civilians. About 1,000 people left the square and marched to the Israeli embassy several kilometres (miles) away.

Chanting "Lift your head high, you are an Egyptian," they demolished the security wall outside the mission with sledge-hammers and a hefty metal bar, as military police looked on.

One protester clambered up the embassy building and removed the flag, throwing it down to the rapturous crowd below.

Protesters set fire to two police trucks around the embassy building, and pelted anti-riot police with stones, an AFP journalist witnessed.

They grabbed several helmets and shields from police and at least one teargas gun, while others invaded and damaged a small police station in the neighbourhood.

Relations between Egypt -- the first Arab country to establish diplomatic relations with Israel in 1979 -- and Israel have been particularly tense since August 18, when Israeli troops killed five Egyptian policemen as they chased militants along the border.

That incident followed a series of Negev desert ambushes that killed eight Israelis.

At the time, outraged Egyptians staged huge protests outside the embassy and called for the expulsion of the Israeli ambassador. Egypt has asked Israel for an official apology and demanded a probe into the deaths.

Since president Hosni Mubarak's ouster in February after a popular revolt, activists have called for a revision of the peace treaty. Mubarak was seen as one of Israel's closest regional allies.