A record number of people were infected with HIV around the world this year, a report says.
Around 14,000 people are infected with HIV every day
Figures from UNAids and the World Health Organization put the number of new infections at five million.
The report also estimates that three million people died from the disease this year.
But it warns that the figures could rise sharply in the years ahead, with Eastern Europe and Central Asia on the verge of epidemics.
Africa hit hardest
The report, which is published ahead of World Aids Day on 1 December, estimates 40 million people around the world are infected with HIV/Aids. Of these, 2.5 million are children.
Around 14,000 people are infected with the disease every day.
Officials say the figures are more reliable than previous year's estimates, following improvements in the way the data is collected.
People living in sub-Saharan Africa continue to be most at risk. About 26.6m people are living with HIV/Aids are in this part of the world.
South Africa, alone, is home to 5.3 million people with HIV - more than any other country in the world. In Botswana, 39% of the population is HIV positive, the report says.
Two out of three new HIV infections occur in sub-Saharan Africa. Three out four deaths from the disease occur in this part of the world.
However, the report also shows that other countries are standing on the verge of major epidemics.
The number of reported infections is rising sharply in China, India, Indonesia and Russia, mostly due to HIV transmission through injecting drug use and unsafe sex.
The report says better prevention programmes are needed to stop the spread.
It says countries around the world must introduce better treatment programmes if millions of deaths are to be avoided.
Dr Peter Piot, executive director of UNAids, praised recent efforts to step up the fight against the disease. However, he said much more needs to be done.
"It is quite clear that our current global efforts remain entirely inadequate for an epidemic that is continuing to spiral out of control.
"Aids is tightening its grip on southern Africa and threatening other regions of the world.
"Today's report warns regions experiencing newer HIV epidemics that they can either act now or pay later - as Africa is now having to pay."
UNAids and the WHO have drawn up a strategy to bring antiretroviral treatment to three million people by 2005 - the so-called "3 by 5" initiative.
Dr Lee Jong-Wook, director general of the WHO, said details of the strategy will be released on World Aids Day next week.
However, he said more money is needed if the strategy is to work.
"This represents an unprecedented drive to increase the number of people receiving treatment," he said.
"For '3 by 5' to succeed, however, and for treatment access to increase further in the future the international community must continue to increase its financial and logistical support."
Nick Partridge, chief executive of the UK charity Terrence Higgins Trust, welcomed the report.
"The HIV epidemic continues to devastate communities across the world and we're increasingly feeling its impact here in the UK.
"Now more than ever, we must step up our efforts to tackle the epidemic in this country, as well as fulfil our responsibilities in the international fight against HIV.
"We will fail if we don't understand that we are all part of a global epidemic," he said.
"Strong political leadership is vital to promote education, access to treatment for all and renewed vigour in the quest for vaccines and a cure."
Derek Bodell, chief executive of the UK's National Aids Trust, said: "Today's statistics continue to cause us concern.
"By now it should be evident to all that HIV does not respect borders."