A awarm of bees attacked half-marathon runners in south-western Japan today, forcing 30 people to be rushed to hospital, rescuers said.

During the race in Saga city, athletes were set upon by the bees as they ran near a river bank, according to one of the local fire departments which dispatched five ambulances because of the incident.

"I have never experienced anything like this before,'' chief rescuer Tomomi Koyanag said.

"Many people complained of sickness although no one collapsed.''

"Some people reported they saw a swarm of bees which looked like a black cloud,'' he said.

One of the runners told public broadcaster NHK: "I heard hollow booming behind my head and soon felt pain. When I saw what it was, it was a honeybee.''

Another runner said bees got inside his shirt, leading to several bites on his neck and back.

Some 3,200 runners took part in the race, organisers said.