"We can't control the situation," Foreign Minister Jose Ramos Horta said, adding that troops from Australia, New Zealand, Malaysia and Portugal had been asked to help "disarm renegade troops and police rebelling against the state."
Some were already boarding flights to the capital, Dili, while others said they could arrive within 48 hours.
East Timor has been plagued by unrest since nearly 600 soldiers - a third of the country's armed forces - were fired in March after going on strike to protest alleged discrimination in the military.
The trouble has escalated into the worst violence since 1999, when East Timor's 800,000 people voted overwhelmingly for independence from Indonesia in a U.N.-organized referendum. Indonesian troops and their proxy militias went on a rampage, killing more than 1,500 people before an Australian-led multinational force stepped in, the AP reports.
Some hard-liners among the dismissed soldiers fled the capital last month after participating in deadly riots, bunkering down in surrounding hills and threatening guerrilla warfare if they were not reinstated.
Clashes flared anew on Wednesday on the west side of the capital, spreading later to the south, near the home of the top military chief, Brig. Gen. Taur Matan Ruak.
One marine officer was rushed to the main hospital in Dili after being shot in the neck, said Antonio Caleres, the hospital director, describing his condition as serious.
The spiraling violence prompted the United States and Australia to order the evacuation of nonessential personnel.
Ramos Horta said he hoped foreign peacekeepers - possibly with a U.N. Security Council mandate - would help restore order to his fledgling nation.
Australia offered up to 1,300 troops, along with three ships, helicopters, armored personnel carriers and heavy airlift capabilities, and said they could arrive by Thursday afternoon.