Calling humanity a threat to the planet, Kenyan environmentalist Wangari Maathai urged democratic reform and an end to corporate greed after becoming the first African woman to collect the Nobel Peace Prize on Friday.

She said sweeping changes were needed to restore a "world of beauty and wonder" by overcoming challenges ranging from AIDS to climate instability.

Maathai founded a campaign that has planted 30 million trees across Africa in a bid to slow deforestation.

"Activities that devastate the environment and societies continue unabated," Maathai, Kenya’s deputy environment minister, said in a Nobel acceptance speech at a glittering ceremony in Oslo City Hall.

"1 call on leaders, especially in Africa, to expand democratic space and buildfairandjust societies, "shesaid.