Immigration officers discovered the group at a hotel in the tourist town of Ha Long on February 19, the Vietnam News Agency reported.
The tourists, aged between 34 and 46 years old, said they wanted to visit Ha Long Bay but did not want to go through a travel company.
They crossed the border in the afternoon of February 19 and booked a Vietnamese driver to take them to Ha Long, which is around a four-hour drive from the border. They said they planned to return to China the next day.
Police also fined the driver VND7.5 million for carrying illegal arrivals.
Nearly 2.7 million Chinese tourists visited Vietnam in 2016, a 51% increase from the previous year.