Damascus, Syria - Syrian rebels shook the world Sunday as they took Damascus after a lightning offensive, sending President Bashar al-Assad fleeing and ending five decades of Baath party rule.

Residents in the capital were seen cheering in the streets as the rebel factions led by the Salafist group Hayat Tahrir al-Sham heralded the departure of "tyrant" Assad, saying: "We declare the city of Damascus free."

AFPTV images from Damascus showed rebels firing into the air at sunrise, with some flashing the victory sign and crying "Allahu akbar", or God is greatest.

Some people climbed atop a tank in celebration, while others battered a toppled statue of Assad's father, Hafez.

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"I can't believe I'm living this moment," tearful Damascus resident Amer Batha told AFP by phone. "We've been waiting a long time for this day. We are starting a new history for Syria."

"After 50 years of oppression under Baath rule, and 13 years of crimes and tyranny and (forced) displacement... we announce today the end of this dark period and the start of a new era for Syria," the rebel factions said on Telegram.

Prime Minister Mohammed al-Jalali said he was ready to cooperate with "any leadership chosen by the Syrian people."

Rebel factions aired a statement on Syrian state television, saying they had toppled the "tyrant" Assad and urged fighters and citizens to safeguard the "property of the free Syrian state".

State TV later broadcast a message proclaiming the "victory of the great Syrian revolution."

The head of war monitor the Syrian Observatory for Human Rights, Rami Abdel Rahman, told AFP: "Assad left Syria via Damascus international airport before the army security forces left" the facility.

HTS said their fighters broke into a jail on the outskirts of Damascus, announcing an "end of the era of tyranny in the prison of Sednaya," which has become a by-word for the most brutal abuses of Assad's era.

The Observatory confirmed "the doors of the infamous 'Sednaya' prison... have been opened for thousands of detainees who were imprisoned by the security apparatus throughout the regime's rule."

Footage posted on social media showed ecstatic people being reunited with family members who in some cases had been incarcerated for decades under the Assad family's rule.

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The commander of Syria's US-backed and Kurdish-led Syrian Democratic Forces (SDF), which controls much of northeast Syria, hailed "historic" moments with the fall of Assad's "authoritarian regime."

US President Joe Biden was keeping a close eye on the "extraordinary events" unfolding in Syria, the White House said.

Led by Abu Mohammed al-Jolani, HTS is rooted in the Syrian branch of Al-Qaeda. Proscribed as a terrorist organization by Western governments, it has sought to soften its image in recent years, and told minority groups living in areas they now control not to worry.

Since the offensive began, at least 826 people, mostly combatants but also including 111 civilians, have been killed, the Observatory said. The UN said the violence has displaced 370,000 people.

Describing Syria's civil war years as a "dark chapter", UN special envoy to Syria Geir Pedersen said in a statement Sunday that "today we look forward with cautious hope to the opening of a new one – one of peace, reconciliation, dignity, and inclusion".

US President-elect Donald Trump posted on his Truth Social platform that "Assad is gone", adding Russia "was not interested in protecting him any longer."

For years Assad was propped up by Russia and Iran, while Turkey, which historically backed the opposition, on Sunday urged a "smooth transition" in Syria.