A single bell tolled across the hot city streets yesterday as mourners packed St Andrew's Cathedral to pray and weep.

Political leaders including the Prime Minister John Howard joined aid workers, families and survivors for a solemn service to grieve for the victims of Boxing Day's tsunami as the nation united for an official day of mourning.

A minute's silence was observed at 11.59am outside after the service, marking the time that the earthquake struck, triggering the tsunami. The scene was echoed in churches, mosques, pubs, backyards and beaches across the country.

Mr Howard and his wife Janette were joined by Acting Opposition leader Jenny Macklin, Shadow Foreign Minister Kevin Rudd, NSW Governor Marie Bashir, and the Lord Mayor of Sydney, Clover Moore. The Premier Bob Carr was represented by Carmel Tebbutt, Minister for Community Services.

Consular representatives from Thailand, the United States, Germany and the Czech Republic attended the service, as did officials from aid organisations working in South Asia. Two Australians who survived the raging waters in Phuket introduced themselves to Cathedral staff before the service began.

Ushers handed out pieces of wattle as people walked into the Cathedral. Mr Howard had requested Australians to wear wattle or other native fauna on the day as a tribute to the dead.

The Prime Minister read from the New Testament passage 1 Peter 5: 5b-11 and Professor Bashir read from Ecclesiastes 3.

Following the minute's silence the Prime Minister and other dignitaries left to sign a condolence book at the Sydney Town Hall.

The Dean of Sydney Phillip Jensen, who led the service, read from Psalm 39 and selected New Testament passages. Sri Lankan couple, Maheesha and Arnjali Sabapathy, ministry trainees at the University of New South Wales, offered prayers for their nation, as did Indonesian couple Alexander Purnomo and Cindy Gunadi, who attend St Andrew's, Bondi Beach.

Also present were 25 Indian members of St Thomas's, Moorebank, several of whom had family or friends affected by the disaster. They said they came to offer their solidarity and show their support for Sydney Anglicans who were donating money to help.

"It's important for us to be here as part of the grieving process," said parishioner Ramabai Chacko. "We know that Anglicans have done so much for our people."

Over 159,700 people are known to have died as a result of the earthquake and tidal waves, including 9,000 foreigners. Many are still missing, feared dead, and one million have been made homeless. The United Nations said its relief operation is their largest ever for a natural disaster.

Recent weeks have been characterised by a worldwide outpouring of generosity and compassion for those who have lost their lives, their homes and their families.

In his sermon Archbishop Peter Jensen likened the current mood in Australia to the outbreak of World War One and Two, when the nation united "for the sake of others".

"Politics, religion and race have been transcended," he said. "On this occasion we have not been moved by bonds of empire and kinship, but by something deeper and truer and better. These are our neighbours, and we knew at once that we had to do all we could to care fo them."

Dr Jensen said the Bible traces such disasters to the "ancient quarrel between man and God, in which the human race chose to live in a world of affliction and pain".

"Humanity is out of joint with both God and the world," he said. "In such a circumstance all of us, innocent and guilty, young and old, believer and unbeliever suffer together.

"But before we charge God with lack of compassion or justice, remember what he did for the world through Jesus Christ."

After the service Dr Jensen said he hoped the centrality of God's word had an impact on people who had heard only criticism of God over the past three weeks.

Offerings given during the service were shared with the Archbishop's Overseas Relief and Aid Fund, which to date has raised $300,000 in aid for affected areas.

Churches across Sydney Diocese also held special services and prayed for the victims.