By October 10, seven family members were dead.
On October 12, an eighth person died. And the final surviving adult who also ate the soup dish, a mother surnamed Li, died on Monday.
Three children in the family had refused to eat the thick noodles made from cornflour, complaining about the taste.
A high concentration of bongkrek acid, a respiratory toxin produced by the bacterium pseudomonas cocovenenans, was detected in the dish.
It was also discovered in the gastric fluid of the adults, the Health Commission of Heilongjiang Province said.
Gao Fei, director of food safety at the Heilongjiang Centre for Disease Control and Prevention, said the toxin can often be fatal.
"It can cause serious damage to many human organs including the liver, kidneys, heart, and brain," Gao told China News Service.
"Currently, there is no specific antidote."
The symptoms of bongkrek poisoning typically begin within a few hours of eating contaminated food, and include stomach pain, sweating, general weakness and eventual coma. Death can then occur within 24 hours.
Bongkrek acid has been implicated in outbreaks of foodborne illness involving coconut and corn-based products in Indonesia and China.
The acid cannot be removed even if thoroughly cooked and there is no medicine available to treat such cases of poisoning, Global Times reported. To avoid poisoning, it added, people should not use soaked or mouldy corn to make food, and not make or eat any food made from fermented grains.
