People pray for peace in All Saints Cathedral in Juba, southern Sudan, Jan. 8, 2011. Around four million southern Sudanese are expected to vote in the coming referendum on Sunday to decide whether the region should remain united with the north or secede to establish an independent state. [Xinhua]

Sudan's southerners began to vote to decide whether the region will remain united with the north or secede to establish an independent state, as a referendum started here on Sunday.

The referendum is a major item in the Comprehensive Peace Agreement (CPA) of 2005, which ended a two-decade civil war between north and south Sudan, that left around two million dead.

The vote started at the polling centers in both south and north at 8:00 a.m. local time (5:00 a.m. GMT) and will last till 5:00 p. m. (14:00 GMT).

Salva Kiir Mayardit, First Vice President of Sudan and President of the Government of South Sudan, cast the first ballot in Juba at a polling station at the museum of John Garang, founder of the Sudan People's Liberation Movement (SPLM).

The security of voting centers must be guaranteed, he said after the voting. "Security forces in the south and north Sudan must make sure the security of the voting."

He noted that the property of the northern Sudanese and foreigners in south Sudan must be protected.

John Kerry, Chairman of the United States Senate Committee on Foreign Relations told Xinhua while he observed the voting process: "I'm very excited. It's very important. I hope it will be a peaceful referendum."

Asked about the controversial issues including border demarcation and the status of the oil-rich Abyei region, Kerry said: "I think the controversial issues can be resolved as we work in good faith."

"The issues can be solved within the six-month transition period," he said.

The voting process will last for seven days to end on Jan. 15, 2011.