A family of eleven elephants have been killed in Kenya in what officials say was the worst such incident in the past three decades.

"We have not lost as many elephants in a single incident since the early 1980s," said Patrick Omondi, head of the elephant programme at the Kenya Wildlife Service (KWS) on Tuesday. "This is a clear signal that things are getting worse."

The corpses of the elephants, including a two-month old baby - all with their tusks hacked off - were found on Saturday in south-eastern Kenya's vast Tsavo East National Park.

Rangers were tracking the poachers in "hot pursuit" but had so far not caught the gang, the Kenyan wildlife rangers said.

"Our initial investigations show that the poachers numbered at least 10 and were armed with an assortment of guns," Omondi said.

The poachers whose weapon of choice is an AK-47 assault rifle, he said.

Officials say that an increase in demand for ivory in Asia, where elephant tusks are used in traditional medicines and to make ornaments, has led to a substantial increase in the killing of elephants in Africa.

In 2012, Kenya lost approximately 360 elephants to poaching, a figure that rose from 289 the previous year, KWS said. At least 40 poachers were killed last year as rangers battled the raiders.

Last week officials in Hong Kong seized more than a tonne of ivory worth about $1.4m in a shipment from Kenya.

Ivory trade is banned under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which is due to hold its next meeting in March, a date that Omondi says has in the past triggered a rise in poaching.

Africa is home to an estimated 472,000 elephants whose survival is threatened by poaching and habitat loss.