The incident occurs in Dong Thanh Commune, Yen Thanh District, Nghe An Province on January 25.
Chairman of Dong Thanh Commune People's Committee, Ngo Van Tuan, told the media that the incident occurred at 8.30 am on Thursday at a house in the area.
Hoang Van Lan, 46, walked to the house of his parents-in-law to call his wife Thai Thi Tinh, 45, home. Tinh went out to meet him and they quarrelled. Lan suddenly stabbed his wife with a knife. His mother-in-law Nguyen Thi Phien, 73, rushed out to prevent him and was also stabbed.
Lan then came in to continue stabbing his father-in-law Thai Duy Lai, 79, before fleeing.
The two women died on the spot while the man suffered serious injuries and has been rushed to hospital.
According to the police, Lan has just been released after serving a jail sentence for robbery. Lan and his wife recently separated and she came to live with her parents. The couple have two sons who work abroad.
Police are further investigating the case.