Most of the alleged kidnappers had been booked for drug-related crimes, the police said.
Three of them were arrested in Hoa Binh Province at a guest house where they kept the girl.
The police, who acted on tip-offs from locals, said they called for the three to surrender but the abductors threatened to fight back and harm the girl.
Police had to use tear gas bombs, but succeeded in rescuing Song Thi Giang, a H’Mong ethnic girl from the northern mountainous province of Son La.
A homemade gun loaded with several cartridges was seized.
Meanwhile, police in Hanoi and Hai Duong Province arrested five other members of the gang, seizing five guns.
The gang, led by 32-year-old Le Van Tho and 25-year-old ex-con Tang Ba Vinh, took the girl to Phu Tho and Quang Ninh provinces as they fled from the police. Most of them had been convicted of drug crimes earlier, police said.
Giang was kidnapped on the night of March 3 by five people who confronted her family with guns and shot at one of them, causing severe injuries, as they tried to chase the car in which the girl was being taken.
They repeatedly called the family later, asking for a ransom of VND500 million (US$24,000) and 1.5 kilograms of heroin.
Colonel Ho Sy Tien from the Ministry of Public Security said the gang appears to have kidnapped the girl to press her father Song A De to repay a debt.
Three months earlier, De had received VND86 million (US$4,140) from Tho, the gang leader, on behalf of a borrower known thus far as Thanh.
It appears that De had given the money to Thanh, but the latter left home and could not be found by those seeking to collect the debt. They decided to pressurize De instead, although the link between either De, Thanh and Tho is not clear.
Tho had reportedly borrowed from his relatives and friends to lend the money to Thanh, a relative of his, but could not collect the debt after visiting De’s house twice, police said.
They also said they are investigating the case further.