Five protesters have died as gunshots were fired and fires lit in the Egyptian capital Cairo's main square.
Hundreds were wounded during the day's protests, the most violent in nine days of protest, amid fierce clashes between supporters of President Hosni Mubarak and opposition demonstrators.
The army has deployed tanks in Tahrir Square after supporters loyal to Mr Mubarak opened fire on anti-government protesters. Mr Mubarak said he would step down in September, but the announcement has not satisfied demonstrators.
Officials in Cairo said 836 people were taken to hospitals, of which 86 were still in care. Five later died.
White House spokesperson Robert Gibbs is urging both government and opposition supporters to show restraint.
A peaceful demonstration in support of Mr Mubarak began about midday. However, a group broke away and fights erupted with anti-Mubarak protesters.
Thousands of people were involved in the running battles. Many were beaten, stabbed or injured by burns from Molotov cocktails. Stones were thrown and the two sides fought with whips and sticks.
A doctor who had been treating people near the square said his team had tended about 400 people, mostly for light wounds such as broken noses and cuts.
The Egyptian army, which earlier urged the protesters to go home, showed no sign of intervening in the fights, though some arrests were made.
A day earlier, Mr Mubarak had announced he would continue in office until the September elections but would not stand for re-election.
United States President Barack Obama says only the Egyptian people can determine the country's leaders, but change must begin immediately and be orderly and peaceful.
The Ministry of Foreign Affairs says more New Zealanders are leaving Egypt as demonstrations in the country escalate.
It is continuing to advise against all travel to Egypt, but says there are still more than 260 New Zealanders in the country, and most of them do not want to leave immediately. Seats on commercial flights from Cairo, Alexandria and Luxor are booked for Thursday and Friday for those who do.