The South Korean government has designated an area hit by a toxic chemical leak as a "special disaster" zone, after more than 3,000 people were treated for ailments ranging from nausea to chest pain.

The September 27 incident at a chemical plant near the southeastern city of Gumi resulted in the leakage of eight tonnes of hydrofluoric acid that caused widespread damage to crops and livestock.

Five people were killed in an initial explosion that led to the leak as workers were unloading the acid from a tanker.

"The government decided to designate the area affected by the leak of hydrofluoric acid as a special disaster zone," the prime minister's office said in a statement on Monday.

The move means villagers in the zone will be eligible for financial aid, tax cuts and compensation.

The statement said the leak had caused "considerable" damage, but added that precise data would only be provided following an ongoing assessment by government officials and experts.

Media reports say more than 3,000 people in two rural villages near the plant have received medical treatment for nausea, chest pain, rashes, sore eyes or sore throats after inhaling toxic fumes from the spilled acid.

The leak affected nearly 80 firms, some of which were forced to shut plants, with the damage estimated at $15.9m, Yonhap news agency said.

It also damaged more than 200 hectares (500 acres) of farmland and affected 3,200 head of livestock.

About 300 villagers have been evacuated to temporary shelters after complaining of health risks, with some reporting blood in their saliva, it said.

Villagers have accused the government of failing to give proper and timely information about the gas leak.