A lion has attacked an elderly man in Kenya's capital, Nairobi, after straying from a nearby national park.

The animal became agitated with people hooting their horns and taking selfies, a wildlife official said.

The lion has returned to the park and the 63-year-old man is in hospital, Paul Udoto, spokesman for the Kenya Wildlife Service said.

The city was put on high alert last month after several lions escaped from the park, causing panic.

A video circulating on social media appears to show the lion wandering along a busy road during morning rush hour.

Rangers are still on the streets of the city in case there are other lions around that have not been spotted, Udoto added.

The park is separated by a main road from densely populated neighbourhoods, including Kibera slum, in the south of the city.

In 2012, four cubs had to be placed in an orphanage after a similar incident led to their mother being killed.

HOW TO CATCH A LION:

In less built-up areas bordering the park:

Manually comb through areas of thick scrub, where lions tend to hide

Use helicopters to spot the animals and then fly low to steer them in a direction away from inhabited areas.

In densely populated areas:

Alert the public to report sightings and stay clear of big cats

Once located, lure the lion out into an open space with goat meat

Once easily visible, a vet should fire a dart with tranquilisers to sedate the cat

Member of the public should never approach or irritate the animals - lionesses with cubs are most dangerous as they will attack if provoked even when not hungry. [Source: KWS senior warden Nelly Palmeris]