The leadership of the 120,000 Armenians who call Karabakh home told Reuters on Sunday that they did not want to live as part of Azerbaijan and that they would leave for Armenia because they feared persecution and ethnic cleansing.
In the Karabakh capital, known as Stepanakert by Armenia and Khankendi by Azerbaijan, crowds of people were loading belongings into buses and trucks as they left for Armenia.
The mass departures were marked by confusion.
An explosion at a petrol storage depot on a road outside the capital injured more than 200 people, local news reports said, quoting Nagorno-Karabakh's ombudsman Gegham Stepanyan.
Most of the injured were in serious or very serious condition and needed to be taken out of the region urgently for treatment, Stepanyan said.
Refugees who reached Armenia told Reuters they believed the history of their breakaway state was finished.
"No one is going back - that's it," Anna Agopyan, who reached Goris, a border town in Armenia, told Reuters.
"The topic of Karabakh is over now for good, I think."
US President Joe Biden said in a letter delivered to Armenian Prime Minister Nikol Pashinyan by US Agency for International Development (USAID) chief Samantha Power that the United States would help address the humanitarian needs.
"You are aware that, unfortunately, the process of ethnic cleansing of the Armenians of Nagorno-Karabakh continues, it is happening right now, and it is a very tragic fact," Pashinyan told Power, according to an Armenian government transcript.
Azerbaijan, which has repeatedly denied any claims of ethnic cleansing, said that the rights of Armenians in Karabakh, a territory internationally recognised as part of Azerbaijan, would be guaranteed.
But thousands of ethnic Armenians have already left.
The Armenian government said on Monday at least 6650 people from Nagorno-Karabakh had crossed into Armenia, up from about 4850 people five hours earlier.
The ethnic Armenian leadership said it would remain in place until all those who wanted to leave what they call Artsakh were able to go.
They urged residents to hold back from crowding the roads out but promised free fuel to all those who were leaving.
Azerbaijan's President Ilham Aliyev hosted his ally Turkish President Tayyip Erdogan on Monday in the autonomous Nakhchivan exclave - a strip of Azerbaijani territory separated from the rest of the country by Armenia.
Aliyev hinted at the prospect of creating a land corridor from the strip to the rest of Azerbaijan through Armenia, which opposes the idea.
The Azerbaijani victory alters the delicate balance of power in the South Caucasus region, a patchwork of ethnicities crisscrossed with oil and gas pipelines where Russia, the United States, Turkey and Iran are jostling for influence.
Since the break-up of the Soviet Union, Armenia had relied on a security partnership with Russia while Azerbaijan grew close to Turkey, with which it shares linguistic and cultural ties.
Russia warned Armenia's Pashinyan that he only had himself to blame for Azerbaijan's victory over Karabakh because he had insisted on flirting with European countries and the US rather than working with Russia and Azerbaijan for peace.
Pashinyan said on Sunday that Russia had not helped Armenia over Karabakh.
Azerbaijan's victory reverses a humiliating defeat the country suffered as the Soviet Union broke up, which left around a seventh of its population homeless and Armenians in control of swathes of territory around Karabakh.
Nagorno-Karabakh has over the centuries come under the sway of Persians, Turks, Russians, Ottomans and Soviets.
It was claimed by both Azerbaijan and Armenia after the fall of the Russian Empire in 1917 and in Soviet times it was designated an autonomous region within Azerbaijan.
