South Sudan celebrated its first day as an independent nation Saturday, raising its flag before tens of thousands of cheering citizens elated to reach the end of a 50-year struggle.

U.S. President Barack Obama called the day a new dawn after the darkness of war, while visiting dignitaries offered both congratulations and prodding for South Sudan and its former ruler, Sudan, to avoid a return to conflict over serious and unresolved disagreements.

"The eyes of the world are now on us," said South Sudan President Salva Kiir, who was inaugurated during a scorching midday ceremony. Kiir stressed that the people of South Sudan must advance their country together, and unite as countrymen first, casting aside allegiances to the dozens of tribes that reside here.

'We're overwhelmed. We did not know that the whole world was going to join us in our celebration.'—David Aleu, South Sudanese citizen

UN Secretary-General Ban Ki-moon, former U.S. Secretary of State Colin Powell and dozens of other world leaders were in attendance.

Sudan President Omar al-Bashir, a deeply unpopular man in Juba, arrived to a mixture of boos and surprised murmurs.

However, Reuters reported that some cheered when he said, "We congratulate our brothers in the south for the establishment of their new state. We share their joy and celebration. The will of the people of the south has to be respected."

"Wow," David Aleu, a 24-year-old medical student, said earlier. "This is a great day for me because it's a day that reflects the suffering that all southerners have had for almost 50 years."

Thousands of South Sudan residents thronged the celebration area, and organizers soon learned they did not have enough seats for all the visiting heads of state and other VIPs. The heat was strong enough that Red Cross workers attended to many people who fainted.

"We're overwhelmed. We did not know that the whole world was going to join us in our celebration," he said.

In a statement Saturday, Foreign Affairs Minister John Baird offered Canada's congratulations and said he would write to his South Sudanese counterpart once the position is filled to establish diplomatic relations with the country.

“After decades of conflict and underdevelopment, this historic occasion represents an important opportunity for the people of South Sudan to build a brighter, better future for themselves," Baird said.

Deepak Obhrai, Baird's parliamentary secretary, attended Saturday's independence ceremony as Canada's representative.

Sudan's history includes two civil wars

The black African tribes of South Sudan and the mainly Arab north battled two civil wars over more than five decades, and some two million died in the latest war, from 1983-2005. It culminated in a 2005 peace deal that led to Saturday's independence declaration.

Thousands of South Sudanese poured into the ceremonial arena when gates opened. Traditional dancers drummed in the streets as residents waved tiny flags. Activists from the western Sudan region of Darfur, which has suffered heavy violence the past decades, held up a sign that said "Bashir is wanted dead or alive." Bashir has been indicted by the International Criminal Court for war crimes in Darfur.

"We came to say welcome to our brothers from the south. We came also to remind the world that the problem in Darfur is continuing," said Nimir Mohammed.

The U.S., China and southern neighbour Uganda all sent delegations.

South Sudan is expected to become the 193rd country recognized by the United Nations next week and the 54th UN member state in Africa.

Though Saturday is a day of celebration, residents of South Sudan must soon face many challenges. Their country is oil-rich but is one of the poorest and least-developed on Earth. Unresolved problems between the south and its former foe to the north could mean new conflict along the new international border, advocates and diplomats warn.

Border contested in several areas

Violence has broken out in the contested border region of Abyei in recent weeks, and fighting is ongoing in Southern Kordofan, a state that lies in Sudan — not South Sudan — but which has many residents loyal to the south. The 2,100-kilometre north-south border is disputed in five areas, several of which are being illegally occupied by either northern or southern troops.

The young government faces the huge challenge of reforming its bloated and often predatory army, diversifying its oil-based economy, and deciding how political power will be distributed among the dozens of ethnic and military factions. It must also begin delivering basic needs such as education, health services, water and electricity to its more than 8 million citizens.

While South Sudan is now expected to control of more than 75 per cent of what was Sudan's daily oil production, it has no refineries and southern oil must flow through the north's pipelines to reach market.

But for Saturday, at least, those problems lay on the back burner. Smiles, singing and dancing instead took precedence.

Adut Monica Joseph waited for the ceremony with her sister and uncle as world leaders arrived. She said she looked forward to a day when women in South Sudan don't face the hardships they have in recent decades. The risk to the mother of death during child birth is extremely high in the poor and underdeveloped rural south.

"I'm very grateful to see many people from other countries," said the 22-year-old. "I'm appreciating that they have come to celebrate with us. I hope when we have independence we shall have freedom and education for women."

With files from CBC News