LONDON -- About 50,000 ethnic Armenians have now fled the disputed enclave of Nagorno-Karabakh, according to local officials, as the exodus triggered by Azerbaijan's takeover of the region appeared to accelerate, with fears its entire population may leave.

More than a third of the population have now left, with nearly 12,000 people leaving overnight, and thousands more continuing to arrive into Armenia on Wednesday morning, in what Armenia's government has called the "ethnic cleansing" of the enclave.

Azerbaijan on Wednesday announced it had detained the former leader of enclave's unrecognized Armenian government as he sought to cross into Armenia. Ruben Vardanyan, a billionaire businessman who made his fortune in Russia, moved to Nagorno-Karabakh in 2022 and served as the head of its government for several months before stepping down earlier this year.

Vardanyan's detention signalled Azerbaijan may prosecute members of the Armenian separatist authorities that remain and will likely further enflame fears among the Armenians remaining there.

The exodus of Armenian civilians has begun following Azerbaijan's successful military offensive last week that swiftly defeated the local Armenian authorities, re-asserting Azerbaijan's control over the mountainous enclave and bringing a sudden end to a 35-year conflict.

Cars, buses and trucks loaded with families and what belongings they could carry have been streaming over the border crossing since Azerbaijan reopened the only road leading out to Armenia for the first time since blockading the enclave nine months ago. The first town on the Armenian side, Goris, was reported flooded with people coming to register as refugees. A 50-mile traffic jam snaked up the mountain road from the enclave, visible in satellite images released by Maxar Technologies.

The death toll from a devastating explosion on Monday at a makeshift gas station used by refugees inside the enclave has reached 68, with 105 people still and dozens more badly injured, local officials said. Helicopters evacuated 168 injured from the region's capital, according to Nagorno-Karabakh's unrecognised Armenian authorities. Shortages of food, medicine and fuel have been reported inside the enclave.

Nagorno-Karabakh is recognised as Azerbaijan's territory but has been controlled by ethnic Armenians since Armenia and Azerbaijan fought a bloody war amid the collapse of the Soviet Union. Hundreds of thousands of Azerbaijanis were driven from the region during that war that ended with ethnic Armenians establishing an unrecognised state, called the Republic of Artsakh.

In 2020, Azerbaijan reopened the conflict, launching a full-scale war that decisively defeated Armenia and obliged it to largely abandon its claims to Nagorno-Karabakh. Russia brokered a truce and deployed peacekeepers to enforce it, which remain deployed.

But last week Azerbaijan launched a fresh offensive that forced the ethnic Armenian authorities to surrender after just two days of fighting and accept the reintegration of the enclave into Azerbaijan. Since then ethnic Armenians have sought to leave, fearing hey will face persecution and violence under Azerbaijan.

Narine Shakaryan, a grandmother of four who arrived at the border on Tuesday told Reuters it had taken them 24 hours to make the 47 mile drive. They had had no food.

"It was horrible, (children) were hungry and they were crying," Shakaryan told Reuters at the border. "We ran away just to survive, that's all."

U.S. Secretary of State Anthony Blinken on Tuesday called Azerbaijan's President Ilham Aliyev to urge him to "refrain from further hostilities in Nagorno-Karabakh" and provide unhindered humanitarian access.

"He called on President Aliyev to provide assurances to the residents of Nagorno-Karabakh that they can live secure in their homes and that their rights will be protected," the State Department said in a readout of the call. He also urged Aliyev to commit to a broad amnesty for Armenians fighters and allow an international observer mission into Nagorno-Karabakh.

Samantha Power, the head of the USAID, visited the border crossing in Armenia on Tuesday and met with refugees there, also calling on Azerbaijan to allow international access to the enclave.