Three men who have fathered nearly 100 children among them are doing their bit for Pakistan's skyrocketing population, which is being counted for the first time in 19 years.

But in a country where experts warn the surging populace is gouging into hard-won economic gains and social services, the three patriarchs are unconcerned. Allah, they say, will provide.

Pakistan has the highest birth rate in South Asia at around three children per woman, according to the World Bank and government figures, and the census is expected to show that growth remains high.

"God has created the entire universe and all human beings, so why should I stop the natural process of a baby's birth?" asks Gulzar Khan, a father of 36, citing one of the strongest influences in the region: the belief that Islam prevents family planning.

Tribal enmity is another factor in the northwest, where the 57-year-old lives in the city of Bannu with his third wife, who is pregnant.

"We wanted to be stronger," the 57-year-old tells AFP, surrounded by 23 of his offspring -- so many, he observes, they don't need friends to play a full cricket match.

Polygamy is legal but rare in Pakistan, and families like Khan's are not the norm, though the beliefs he holds are widespread.

The last census, held in 1998, showed Pakistan had a population of up to 135 million. Estimates suggest the new census -- carried out earlier this year, with the preliminary results due by the end of July -- will put the figure closer to 200 million.

The economy is expanding faster than it has in a decade, and last month Islamabad hiked its development budget by 40 percent.

But observers have warned the population boom is negating any progress, using up valuable resources in a young country where jobs are scarce and nearly 60 million people live below the poverty line.

"It definitely is a problem because it is affecting health outcomes adversely and also eating into development gains," says Zeba A. Sathar, country director for the UN population council.

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Sathar predicted the census would show growth has slowed due to lower fertility rates, though she added it would remain among the highest rates in the region.

"There has to be a clear enunciation of need to slow growth as a positive policy lever," she said. "And then next a good, effective health system that provides information and services of quality."

- 'God will provide' -

Khan's brother, Mastan Khan Wazir -- one of his 15 siblings -- also has three wives. So far, Wazir has only fathered 22 children but, like his brother, he says his grandchildren are too numerous to count.

The 70-year-old, with his bushy moustaches and bejewelled fingers, is a minor celebrity in North Waziristan tribal district, where his blinged out jeep -- done in the style of Pakistan's famous "jingle trucks", with Pashto music pouring from the stereo -- is a familiar sight.

"God has promised that he will provide food and resources but people have weak faith," he tells AFP, wearing a traditional Waziristani turban.

In the southwestern city of Quetta in Balochistan province, Jan Mohammed -- the father of 38 children -- agrees, despite having previously called on the government to provide resources for his family.

Jan spoke with AFP in 2016 to voice his desire for a fourth wife as he continues his mission of having 100 children. No woman has yet agreed, he says, but he has not given up.

"The more Muslims grow, the more their enemies will fear them... Muslims should go for more and more children," he said.

- Empowering women -

Denied their husbands' permission to speak, none of the three men's wives could give their views on family planning in Islam.

But there is already "abundant" awareness in Pakistan about the need for birth spacing, or allowing a woman's body to rest for at least 18 months between pregnancies, Sathar said.

"The need is for clear information about the methods available, how they work, their possible side effects and where to get them. That is missing," she added.

Giving women more of a choice in the matter could help, argues Aisha Sarwari, a feminist activist who has previously written on population and women's rights.

"Access to birth control for women can be a game changer," she told AFP. "Ultimately the impact is that there are more resources to go around ... Empowered women have fewer children, and this creates a mindset that leads to prosperity within families that is likely to be emulated across communities."

Khan, at least, admitted there could be some benefits to slowing down.

For one thing, tribal enmity in the northwest has decreased in recent years, he said. "Now, with the grace of God, the situation has changed -- war and fighting is finished -- so, now, a decrease in the population would not be bad."

It would also free him up for other leisure activities, he says, adding wistfully: "If one had fewer children, one would have more time to make love with his wives."