Torrential downpours in a city in Hunan province, as well as the region's topography and soil conditions, have resulted in several deaths, local authorities said on Friday.

Flooding tied to Typhoon Gaemi that made landfall in China on July 25 has led to at least 30 deaths and 35 others missing in Hunan's Zixing. Affected residents number some 118,000, local authorities said during a news conference.

Heavy rains also caused more than 1,300 road collapses, power outages in nearly 150 villages and disrupted communications across 78 townships. About 1,600 homes collapsed and 76,300 mu (5,087 hectares) of farmland was destroyed.

"Losses are still not completely accounted for," said Kan Baoyong, mayor of Hunan's Chenzhou that administers Zixin.

Xiao Yingbin, head of the geological disaster prevention and control center at the Mineral Resources Survey Institute of Hunan Province, said that the intensity of rainfall related to the typhoon was "unprecedented".

"The average accumulated rainfall in Zixing reached 412.7 millimeters, with the highest rainfall hitting a historical record of 673.9 mm. The maximum rainfall per hour also exceeded historical records to hit 132.2 mm," Xiao said.

Torrential rains triggered landslides and debris flows, which compounded difficulties in launching rescue efforts, he added.

Meanwhile, villages and townships hit hardest by the disaster are located in southeastern parts of the city, where slopes are steeper and the terrain higher and more seriously eroded.

Another feature of the severely affected areas is the soil condition.

The erosion of granite has left topsoil with a looser texture. Heavy precipitation within a short period of time quickly infiltrates the soil, increases its weight and raises the risk of landslides, he said.

Cao Zhongsheng, an emergency management official in Chenzhou, said that 34 rescue teams comprising 986 people and over 80 rescue drones have been dispatched.

Kan, the mayor, said that more than 13,000 affected residents have been relocated and nearly 700 trapped people have been rescued and moved to safe places so far.

As of 8 pm on Thursday, eight of the nine key blocked roads had been cleared and power supplies had been restored to the majority of households.

More efforts will be made to ensure that all key roadways are cleared, and power supplies and communications restored in all villages, he said.

Zhu Youfang in Changsha contributed to this story.