Malawi's government is calling on all sexually active people in the country to take an Aids test, saying this would help it combat the pandemic.
Malawi's president says Aids is blocking the fight against poverty
About 14% of Malawi's 12m people are believed to be HIV-positive but more accurate figures would help planning and enable people to get treatment.
The campaign is to be focused on rural areas that are usually beyond the reach of the state's health services.
Malawi's government says Aids is one of its biggest challenges.
President Bingu wa Mutharika has said the disease is a major threat to efforts to drag the nation out of poverty.
In May, the World Health Organization issued new guidance, saying that anyone seeking medical treatment in countries where HIV was rife should be tested, unless they "opted out".
However, no test should be done against a person's wishes or without their knowledge, the guidelines stress.
The WHO said that 80% of people with HIV in sub-Saharan Africa did not know they had the virus.
The BBC's Peter Greste says nobody is predicting that the entire nation will show up at the test sites in the next seven days but the health ministry has distributed about 300,000 testing kits around the country to cope with the expected demand.
"We want to encourage Malawians to go for the tests. We also want to take advantage to reach them with correct information on HIV prevention, treatment, care and support," ministry of health official Mtemwa Nyangulu told the AFP news agency last week.
Until now, testing was done only if a person requested it.
The authorities say only 15% of the six million sexually active Malawians have had an Aids test and know their status.
On Saturday, Tanzania's President Jakaya Kikwete publicly took an Aids test at the start of a similar campaign.