Livestock herders living near Ol Doinyo Lengai in northern Tanzania have abandoned pastures on the slopes of the mountain after tremors believed to be the result of volcanic activity, a government official said.

"We have advised residents of Engaresero village who had taken their livestock to pastures on the slopes of the mountain to move away from the area," Jowika Kasunga, the commissioner in charge of Ngorongoro district, where the mountain is situated, told IRIN on 20 July.

He said the village, at the foot of the mountain, was inhabited by an estimated 5,000 people, some of whose houses had developed cracks after the intermittent tremors between 12 and 18 July.

The 'swarm' of earthquakes has caused alarm in several parts of Tanzania and neighbouring Kenya.

"People are worried but they are still in their homes," said Kasunga. He denied media reports that the mountain had spewed lava, forcing people to flee. However, tourists have been advised to avoid the area.

He said local authorities had embarked on a disaster awareness campaign that focused on what people should do in the event of a major earthquake and advising them to evacuate if the volcano erupted.

Christine, a resident of Arusha, about 100km southeast of Ol Doinyo Lengai: "Yesterday [19 July] there was an announcement on the television and the radio. We were advised not to stay near tall buildings or trees, and try to seek protection.

"At the time of the first tremor I was at home, in my bed. I just stayed in bed and waited for the tremor to end. If it had lasted longer, or if it had been stronger, I might have gone outside," she said.

"Of course I am afraid, I am not very sure about what is going to happen," said Christine, who gave only her first name. She said the wall of a government building in Arusha had cracked.

Tanzania's chief geological expert on 19 July advised residents living close to the Ol Doinyo Lengai to stay at least 50km away from the mountain.

As a precaution, Abdul Mruma, chief executive officer of the Geological Survey of Tanzania, added: "The safest distance to stay away, however, is 100km."

The most powerful quake, on the afternoon of 17 July, was estimated at 5.9 on the Richter scale.

The US Geological Survey, which has been monitoring the tremors, said the information available was "not sufficient to determine if the current activity reflects a geologic process that might lead to a change in the eruptive behavior of Ol Doinyo Lengai". The last major eruption of the volcano was in 1966.

Mohammed Mhita, the director-general of Tanzania's Meteorological Agency, also played down fears of an imminent eruption.

In neighbouring Kenya, authorities stepped up disaster preparedness after the quakes caused panic in the capital, Nairobi.

Government spokesman Alfred Mutua said all office buildings, schools, factories, apartment blocks and other buildings should have emergency evacuation procedures and contingency plans ready.