South Sudan was set to wrap up a week-long independence vote on Saturday confident one of the world's poorest regions is now securely on the path to becoming its newest nation state.

A handful of voters trickled to the polls on the final day of the landmark referendum that is set to turn the page on five decades of conflict between the mainly Christian, African south and the mainly Arab, Muslim North.

But so many people turned out on the first four days that the 60 per cent threshold set for the referendum to be valid by the 2005 peace agreement which ended the last, 22-year civil war was passed on Wednesday evening and there were few people left to vote.

That hurdle had been the only real question mark over the poll — in a general election last April the pro-independence former rebels of the Sudan people's liberation movement took a full 93 per cent of the vote.

Few analysts expected the margin of victory to be much different this time round.

At the polling station set up by the tomb of veteran rebel leader John Garang in the regional capital Juba, chief returning officer Manyang Malook Akot said 88 per cent of the 12,258 registered voters had already cast their ballots by the close of polls on Friday.

Referendum observer Isaac Kenyi said that in sharp contrast to the jubilant crowds that had overwhelmed polling stations in the first four days, just two voters had turned up in the first 20 minutes of the 10 hours of polling on Saturday.

He said less than 100 had voted on Friday and that he did not expect more to do so before the close of polls at 6.00 pm (1500 GMT) on Saturday.

"We could close at 5.00 pm," he said, alluding to the polling hours originally set before organisers ordered a one-hour extension from Tuesday in the face of the huge queues of eager voters still waiting outside polling stations at the close on the first two days.

The south's ruling party had taken every opportunity to appeal to the consciences of an African nation still blighted by the devastating 1983-2005 war.

"The final walk to freedom, 2.5 million lives paid," screamed banners and flyposters across the region.

And they did walk for hours or even days, in some cases more than once.

"The only complaints were those who left disappointed after waiting so long in the sun but who did not get to vote because the time ran out," the governor of lakes state, West of Juba, Chol Tong Mayay, had told AFP on Monday.

"Many had to walk three or four hours each way to reach a centre."

George Emanuel told AFP it had taken him six days to reach Juba from the Northern city of El-Obeid as he cast his vote on Saturday.

The close of polls was to sound the starting pistol for the massive logistical operation of collating the result, which is not expected before in February.

UN helicopter crews were to assist referendum organisers in picking up ballot papers from the remote countryside of a vast, underdeveloped region which has just 40 kilometres (25 miles) of paved road for an area the size of France and Belgium combined.

On the streets of the Sudanese capital Khartoum, there was a sense of rueful resignation that the nearly nine million people of the south were poised to break away — and with them some 80 per cent of Sudan's oil reserves — leaving the north's 32 million people to go it alone.

"I feel sad," said Mustafa Mohammed a young tax officer in Khartoum. "I am not for secession. If it were not for politics, we would still be united."

In the face of the looming prospect of the loss a big chunk of its oil revenues after the partition of Africa's largest nation, the Khartoum government announced ahead of the independence vote that it was reducing state subsidies on fuel and sugar and tightening government spending.

The austerity package triggered clashes between students and the police in the north on Wednesday and Thursday, although not on anything like the scale of the deadly unrest that has rocked Tunisia for the past two months, prompting veteran President Zine El Abidine Ben Ali to take refuge in Saudi Arabia.