President John Magufuli urged Tanzania's women to "set your ovaries free" and bear more children as a way to help boost the economy into a regional powerhouse, a step critics say will instead worsen inequality and poverty.

Key points: Mr Magufuli launched an industrialisation campaign that helped drive economic growth

Mr Magufuli launched an industrialisation campaign that helped drive economic growth Tanzania's economic growth rate has averaged 6-7 per cent annually over the past decade

Tanzania's economic growth rate has averaged 6-7 per cent annually over the past decade The nation has one of the world's highest birth rates — around five children per woman

"When you have a big population you build the economy. That's why China's economy is so huge," he said late on Tuesday, citing India and Nigeria as other examples of countries that gained from a demographic dividend.

"I know that those who like to block ovaries will complain about my remarks. Set your ovaries free, let them block theirs," he told a gathering in his home town of Chato.

Since taking office in 2015, Mr Magufuli has launched an industrialisation campaign that has helped drive economic growth, which has averaged 6-7 per cent annually over the past decade.

But he has said a higher birth rate would achieve faster progress.

At the same time, the East African nation of 55 million people already has one of the world's highest birth rates — around five children per woman.

Data from the UN population fund UNFPA shows Tanzania's population is growing by about 2.7 per cent per year.

But most public hospitals and schools are overcrowded and many young people lack jobs.

President says family planning is for the 'lazy'

Mr Magufuli has overseen a period of economic growth in Tanzania. ( Reuters: Sadi Said )

UNFPA says about a third of married women in Tanzania use contraceptives, but Mr Magufuli has criticised Western-backed family planning program implemented by the health ministry.

Last year the President said curbing the birth rate was "for those too lazy to take care of their children", and the health ministry barred broadcasting of family planning ads by a US-funded project.

While Tanzania's poverty rate — people living on less than $US1 a day — has declined to about 26 per cent as of 2016, the absolute number of poor citizens has not because of the high population growth rate, according to the World Bank.

Opposition leaders in Tanzania have criticised Mr Magufuli's stance, saying the country's already-rapid population growth is a time bomb, and disapproving remarks surfaced on social media.

"As a modern woman I can't believe this … especially coming from him [the President]," one Twitter user said.

Opposition leaders in Tanzania have criticised Mr Magufuli's stance, saying the country's already rapid population growth is a time bomb. ( Supplied: US Africom )

Others said it was simply bad economics for Mr Magufuli to urge Tanzanians to have more babies.

"High population growth in Tanzania means increased levels of poverty and income inequality," said a rights activist based in Dar es Salaam who asked not to be named to avoid possible repercussions from the Government's ongoing review of registration of non-governmental organisations.

"Women's ovaries should never be used as a tool for seeking economic prosperity."

Reuters