A powerful rendition of 'Amazing Grace', accompanied by a 46-piece orchestra, provided the perfect opening to the 21st annual Hillsong Conference in Sydney, Australia.

More than 30,000 Christians from 68 nations representing 19 denominations packed the opening night sessions which were held at the Acer Arena in Sydney.

Hillsong's Senior Pastor, Brian Houston, said that one of the key themes of the conference is 'justice'.

He said, "God tells us that standing against injustice and speaking up for the disenfranchised is the responsibility of every Christian. This conference will help highlight the impact we can make if collectively we decide to take this responsibility seriously."

In the opening session, delegates heard from Pastor Gary Skinner, founder of Watoto Child Care Ministries about the plight of Aids orphans and child soldiers in Uganda.

He urged church leaders to rise up and take responsibility for the desperate needs in the world today.

"I believe it's not the responsibility of movie stars or pop idols or the government to care for God's children. It's our responsibility," Pastor Gary said.

"While the government might be able to put a little food in their belly and a little bit of education in their brains and a roof over their head and some clothes on their back, there's not a government in the world that can put Christ's love inside the heart of a child and give them dignity and value. Only we can do that. So we must hear God's call and respond in loving and practical ways, and we must do it now."

The Watoto Children's Choir filled the Acer Arena with their blend of soulful African rhythms and contemporary gospel music. Watoto works to rescue Aids orphans in Africa, today they house more than 1,700 children in purpose-built villages providing homes, schools and clinics.

The Skinners are planning to build a new village in Gulu in northern Uganda to rehabilitate former child soldiers who were kidnapped and trained to kill by the rebel army during years of bitter civil war.

Last night, the Skinners were presented with a cheque for $740,000 donated by the people of Hillsong Church over one weekend for Watoto's efforts in northern Uganda.

The conference continues until Friday night with some of the finest church leaders and Christian musicians including Grammy Award winner, Steve Curtis-Chapman, best-selling author John Bevere, and the Rev TD Jakes.