Local police are investigating the murders of five family members in South China's Guangdong Province.

The case occurred Thursday morning at 2 am in an apartment in a Fu'an residential community in the Nanhai District of Foshan.

Sources at the Nanhai Public Security Bureau told China Daily on Friday five members of a family, including a 7-year-old boy and his mother, surnamed Cai, had been killed.

"I heard a very huge sound downstairs when I was watching TV," said a young man who lives one floor above the Cai's. "Then I heard a boy cry."

"I thought it might be a quarrel between the couple," the neighbour said.

Based on the initial investigation, it might have been a revenge murder, according to a local police officer who gave the surname Xiao.

"It is one of the most serious murder cases in recent years in the city," he said. "We will spare no effort in finding the cause as soon as possible."

Apart from mentioning the boy and his mother, Xiao did not disclose details of the other victims.

Neighbours said Cai and her husband ran a restaurant and a drug store near the residential community. "Unlike her husband, Cai had a bad relationship with customers," said a young woman who used to visit Cai's restaurant.

Cai's husband, surnamed Huang, was not home on the day of the murders, said sources with the local public security authority.

Editor: Yan