South Africa's 2011 census started on Monday, with the homeless and babies born after midnight being the first to be counted.

Questionnaires were also dropped off at all hotels, guest houses, lodges and other accommodation. These had to be completed by hotel managers and guests who spent the census night there.

Stats SA's Trevor Oosterwyk told the SABC census teams would start going into the streets on Monday morning.

He said he understood people were suspicious of the field workers, but assured they had been vetted.

"We have made sure that all... field workers have been vetted... there are no people with criminal records," Oosterwyk told the broadcaster.

President Jacob Zuma urged all South Africans to ensure they were counted, the SABC reported.

"It will help us to plan well to build a better life for all," said Zuma.

School children and teachers would help ensure every household in South Africa was counted, Stats SA said in a statement. As part of the learner ambassador programme, pupils would report whether their families had been counted to their teachers.

Enumerators would check with the schools whether any households had been missed. These would be visited during the census mop-up period from November 1 to 13, said Stats SA.

On Friday, Stats SA said people were legally obliged to answer all questions during the census, despite a security company saying otherwise.

People would be asked questions concerning their income, place of work, and past addresses.

Each field worker was expected to spend at least 45 minutes at a house. Part of the census was to gather information on the economic standing of the various provinces.

The census would last until October 31. People can call 0800-110-248 to make sure that enumerators are genuine.