Syrians rejoiced into the night as fireworks exploded on the first Friday -- the Muslim day of rest and prayer -- since the ouster of president Bashar al-Assad.
More than half a century of brutal rule by the Assad clan came to a sudden end on Sunday, after a lightning rebel offensive swept across the country and took the capital.
Assad's fall has also led to fast-moving diplomatic developments.
Turkey announced it will reopen on Saturday its embassy, closed since 2012 amid Turkish government calls at that time for Assad to step down.
A Qatari diplomat said a delegation from the Gulf emirate is to visit Syria on Sunday to meet officials of the transitional government and "take the necessary steps to reopen the embassy and discuss enhancing aid delivery".
Unlike other Arab states, Qatar never restored diplomatic ties with Assad after a rupture in 2011.
Assad fled Syria, closing an era in which suspected dissidents were jailed or killed, and capping nearly 14 years of war that killed more than 500,000 people and displaced millions.
Abu Mohammed al-Jolani, head of the Islamist group Hayat Tahrir al-Sham (HTS) which spearheaded the offensive, had called on Syrians "to go to the streets to express their joy".
They continued all afternoon and into the night, AFPTV live images showed from Umayyad Square in Damascus which was jammed with vehicles, people, and waving flags as fireworks shot into the air.
In the early days of Syria's uprising in 2011, pro-democracy protesters gave their Friday gatherings a different name every week.
On the first such day after Assad's fall they called it: "Friday of victory".
Thousands flocked to the capital's landmark Umayyad Mosque, some raising the three-star Syrian independence flag which none dared wave in the capital during Assad's repressive rule.
Exhilarated crowds chanted, "The Syrian people is one!"
- Unimaginable -
Crowds also gathered in the squares and streets of other Syrian cities, including Homs, Hama and Idlib.
There was a festive and relaxed atmosphere as hundreds rallied in the main square of Syria's second city Aleppo, a scene of fierce fighting during the country's civil war, AFP correspondents said.
A huge billboard depicting Assad and his father Hafez was set on fire.
"The Assad father and son oppressed us, but we have liberated our country from injustice," a white-bearded policeman at the scene said.
Ahmad Abd al-Majed, 39, an engineer who returned to Aleppo from Turkey, said many shed "tears of joy and happiness".
"Syrians deserve to be happy," he said.
In the southern city of Sweida, the heartland of Syria's Druze minority, Bayan al-Hinnawi, 77, never believed he would live to see such a day.
"It's a wonderful sight. Nobody could have imagined that this could happen", said Hinnawi, who spent 17 years in prison.
Sunni Muslim HTS is rooted in Syria's branch of Al-Qaeda and designated a terrorist organisation by many Western governments, which now face the challenge of how to approach the country's new leadership.
The group has sought to moderate its rhetoric, and the interim government insists the rights of all Syrians will be protected -- as will the rule of law.
The European Union was seeking "to establish contacts" with the new rulers in the near future, an EU official told AFP on condition of anonymity.
The United Nations refugee agency said the new government had sent "constructive" initial signals, including asking the organisation to stay in the country.
Leaders of the Group of Seven (G7) democratic countries, who met virtually on Friday, expressed hope for "a peaceful and orderly transition through the definition of an inclusive political process" in Syria.
- Disappeared -
Inside much of Syria, the focus is turning towards unravelling the secrets of Assad's rule, and particularly the network of detention centres and suspected torture sites.
Syrians have descended upon prisons, hospitals and morgues in search of long-disappeared loved ones.
"I turned the world upside down looking," Abu Mohammed told AFP as he searched for news of three missing relatives at the Mazzeh airbase in Damascus.
"We just want a hint of where they were."
The International Committee of the Red Cross said it has documented more than 35,000 cases of disappearances during Assad's rule, with the actual number likely far higher.
While Syrians celebrate the end of Assad's brutal government system, they face a struggle for basic necessities in a country ravaged by war, sanctions and runaway inflation.
On Friday, the EU announced the launch of an "air bridge" operation to deliver an initial 50 tonnes of health supplies via neighbouring Turkey.
- Israel ready to stay in buffer zone -
Assad was propped up by Russia -- where a senior Russian official told US media he has fled -- as well as Iran and Lebanon's Hezbollah militant group.
Turkey's Foreign Minister Hakan Fidan told Turkey's private NTV television that his country had urged Russia and Iran not to intervene militarily against the rebel advance "to ensure minimum loss of life".
The rebels launched their offensive on November 27, the same day a ceasefire took effect in the Israel-Hezbollah war, which saw Israel inflict staggering losses on Assad's Lebanese ally.
Both Israel and Turkey, which backs some of the rebels who ousted Assad, have since carried out strikes inside Syria.
Israel has sent troops into a UN-patrolled buffer zone that separated Israeli and Syrian forces on the Golan Heights, in a move the UN said violated a 1974 armistice.
The army has been ordered to "prepare to remain" there throughout the winter, Defence Minister Israel Katz's office said on Friday.
In Baghdad on Friday as part of a Syria-focused tour, US Secretary of State Antony Blinken said that "as Syria transitions from the Assad dictatorship to hopefully a democracy", it should "not become in any way a platform for terrorism".
The United States has troops in both Syria and Iraq as part of a coalition against the Islamic State jihadist group.