At least six people died and dozens went missing when a mine was flooded in northern Tanzania on Saturday, a police official told AFP.
"We have so far received six bodies and we are still searching for others," said the official, who was at the scene but declined to be identified.
"The owners of the pits said 87 were underground at the time of the floods," he added.
The accident took place overnight at the Mirerani Tanzanite gemstone mines near the northern city of Arusha, around 450 kilometers (280 miles) north of the capital Dar es Salaam.
"We have the reports of the missing miners and rescuers have been rushed to the scene," Manyara regional commissioner Henry Shekifu told AFP.
"There have been heavy rains for the last seven days in the area. Similar cases occurred in the past, but this is worse because it involves a lot of people," he added.
Shekifu, the region's top government official, confirmed the current death toll stood at six.
Miners heading back to Arusha from the Mirerani and neighbouring pits said they feared their colleagues were dead.
Torrential rains hampered communications in the region as well as the rescue operation, with many vehicles involved in the effort stranded several miles from the site of the disaster.
A lack of equipment also impeded the rescue operation, which was expected to continue overnight.
Tanzanite, a purple-blue shimmering stone, has been found only in northern Tanzania and in 2005 a leading gemstone miner said it unearthed the world's largest tanzanite stone weighing about three kilograms (6.6 pounds).
The lure of striking riches has drawn thousands of miners to Mirerani, which resembles a gold-rush town dotted with brothels, bars and hardware stores supplying the miners.
Tanzanite is believed to be limited to east Africa's Rift Valley region and the pits where the accident happened are located in the heart of Maasai land, a short distance from Mount Kilimanjaro.
The gemstone was discovered by Maasai tribesmen in 1967.
The east African nation's mining sector has expanded rapidly over the past decade after it adopted liberal economic policies in the mid-1980s.
Tanzania is the continent's third-largest gold producer after South Africa and Ghana and is also rich in diamond, emerald, ruby and sapphire.
The mining sector contributes less than three per cent of the nation's GDP but the rate should reach 10 per cent by 2025 according to a development plan outlined by the government.