An elderly woman is fighting for her life after being stung more than 500 times by a swarm of killer bees in the south-western United States.

Between 30,000 to 40,000 bees attacked the 77-year-old woman as she walked past their hive near her home in Las Vegas.

The woman was stung on her arms, chest, face and head. Eyewitnesses heard her screaming and called the rescue services.

Firefighters drove an estimated 200 bees from her body by dousing the woman with water.

Two men were also stung as they tried to rescue the woman.

A fire brigade spokesman said the woman was in shock by the time they arrived and was admitted to hospital, where staff used tweezers and duct tape to pull the stings from her body.

It is thought the bees had been attracted to something in her bag.

The journey north

Experts say the bees were Africanised honey bees - more commonly known as killer bees.

The African bees were originally brought to South America from southern Africa in 1956.

They were crossbred with European bees to improve their tropical hardiness, but some escaped from the laboratory a year later, and began to migrate north.

This type of bee has killed an estimated 1,000 people on their journey, colonising ever greater areas of Central America, Mexico and California.

To the naked eye, the Africanised bee looks the same as the European honey bee, and individually, their venom is no more potent.

But the Africanised bees' sting in greater numbers, are more easily agitated, and are not intimidated by people.

They are also more defensive in reacting against perceived threats to their hives, and will fly up to a kilometre (half a mile) in pursuit of a target.