Dressed in a white jumpsuit, mittens and socks, the baby girl lay quietly in the Malaysian heat.

"I picked her up and she smiled," said Hartini Zainudin, recalling the hot Saturday morning that changed her life.

Hartini is well known in Malaysia as a child rights activist who rescues unwanted babies.

She thought this was another of those cases. But then the woman who had been caring for the baby at a house in the port town of Klang, about an hour's drive from Kuala Lumpur, got down to business.

For $3,000, she said, Hartini could take the baby home immediately and raise her as her own.

"They said, 'You can buy her … or she'll go to Thailand'," Hartini recalled.

She stepped outside and phoned a fellow activist, who told her that trafficking gangs sometimes maim young children before forcing them to beg in Thailand.

Hartini's decision was instant. She walked back into the house and agreed to buy the little girl, another deal done in Malaysia's lucrative underground baby trade.

An exclusive Al Jazeera investigation for 101 East has revealed that baby selling rackets are thriving in Malaysia.

A complex web of traffickers and doctors is turning the youngest, most vulnerable human lives into commodities, putting them up for sale to the highest bidder.

In this Southeast Asian nation, where legal adoption can take years, people are handing over thousands of dollars to baby sellers and turning to corrupt officials to help register the children they buy as their own.

A baby's price can range from about $400 to $7,500, with their value determined by race, skin colour, gender and weight.

"The lighter skin, if a male, higher price. The darker skin, a girl, lower price. And then if you're a mix, higher price. This is how it works," explained Hartini.

The babies offered for sale come from a variety of women. Some are poor migrant workers who, by law, are not allowed to have children in the country. Others come from Malaysian women, including some who are forced to give up their babies to avoid the stigma associated with having a child out of wedlock.

The buyers are often childless couples desperate to start a family and frustrated with the country's convoluted adoption procedures. But activists say some babies are bought for more sinister purposes, sometimes by syndicates who groom children for paedophiles.

During a four-month undercover investigation, Al Jazeera discovered just how easy it is to find a baby to buy in Malaysia and to obtain the false documents required to change a baby's identity.

Websites and social media pages offer numerous babies who are "in need of a loving home". The posts detail the baby's due date, expected medical costs and the so-called "consolation fee" to be paid to the birth mother.

"You can choose your baby online," Hartini explained. "In a lot of the cataloging for baby selling, you'll have Chinese, Malay … it's like a supermarket."