The first four of the elephants due to be relocated over the next 10 days were shot with tranquilizer darts from a helicopter near Narok town, some 150 kilometres south of Nairobi, a notorious zone for human-wildlife conflict.

Once the giant animals fell asleep, conservationists carefully winched them up by crane onto trucks for the journey to the Maasai Mara, from where they had been cut off by widening settlement, increasing farming and deforestation.

"The greatest challenge to Kenyan wildlife conservation today is Kenya's population growth," said Kenya Wildlife Service (KWS) director Julius Kipng'etich.

Workers splashed the elephants with water to cool them before giving another injection to wake them up, ready for their 150-kilometre truck journey to the Maasai Mara.

If the operation is a success for the first 50 animals, KWS plans to move 200 of them in all.

"The area where the elephants are being moved from can no longer hold 200 elephants in view of the increasing habitat loss due to conversion of areas used by elephants into agriculture," the KWS said in a statement.

In the last decade, elephants have been responsible for more than 50 percent of the 9,299 cases of human-wildlife conflict in the Narok area, according to the wildlife body.

"The future of conservation will be very challenging because it forces us to contain animals in a very small space... which is unfortunate," Kipng'etich said.