Kenya is moving 50 elephants to a new home after overcrowding in the Mwea National Reserve has seen the creatures stray into nearby human settlements and damage local ecosystems.

The last national wildlife census recorded 156 elephants at Mwea, more than three times the reserve's capacity. As a result, elephants have strayed into nearby villages, damaging crops, infrastructure and property.

During a two-week mission to relocate the animals from the 42 square km Mwea reserve to the more spacious Aberdare National Park, wildlife specialists, travelling in helicopters, sedated elephants with tranquillizer darts, bound their feet and loaded them onto a caged truck for the four-hour drive northwest.

Kenya's elephant population dropped dramatically a few decades ago because of rampant poaching to supply ivory. But years of conservation efforts have now boosted numbers, with some parks like Mwea National Reserve grappling with overcrowding.

"The elephants have really troubled us," said nearby villager Pauline Njue. "Now we feel relieved, especially because our children could not walk to school early in the morning for fear of running into the elephants."

The relocation will reduce the harm caused to the environment when a large number of animals live in a small ecosystem, said Isaac Lekolool, Kenya Wildlife Service's head of capture and veterinary services.

Relieving the pressure from the elephants could allow other species to thrive, he said.

The elephants all have GPS collars so wildlife rangers can track their movements over the next two years and monitor their adjustment to their new surroundings. The relocation is due to be completed on Wednesday.