Six lions were speared to death overnight on the outskirts of the Kenyan capital after they strayed from the city's national park and killed four goats, the Kenya Wildlife Service said Wednesday.

Two adult lionesses, two young adults and two cubs were killed by a mob after they invaded a settlement in Kitengela on the outskirts of the park, KWS said.

The wildlife authority said it had dispatched rangers and a veterinary capture team to search for the cats after receiving a report from the community that lions had strayed from the park.

"While the search was on, the lions were killed by the mob," KWS said in a statement.

At the beginning of the year at least two lions were killed in similar circumstances in Kitengela.

Nairobi National Park is only partially fenced off to allow animals to move around and migrate.

"Nairobi National Park is a seasonal park and during rainy seasons, herbivores stray out of the park and lions pursue them. In the pursuit lions encounter livestock," the wildlife authority said.

"The killing is a big loss to the economy given that lions enjoy an iconic status as one of the 'Big Five' which are a big draw for tourists who visit Kenya," KWS went on.

Kenya has been losing 100 lions a year for the best part of the past decade, leaving the country with just 2,000 of its famous big cats.

"This implies that the country could have no wild lions at all in 20 years," KWS said.