Huang Weiming, 51, and Huang Cheng Lan, 48, who work for Vietnam Baodi Technology Company in the Cao An Industrial Park in Cam Giang District, were found riding on a street last Saturday despite a lockdown since February 5 amid a surge in infections.
Authorities have called on the public to only leave home to buy necessities like food and medicines or for emergencies.
The duo admitted to local authorities they had been out for "unnecessary" reasons, Lao Dong newspaper reported.
Authorities in Hai Duong have installed surveillance cameras on major streets in some high-risk areas to help the police verify public compliance with pandemic prevention measures.
Vietnam has had 791 Covid-19 cases in 13 localities since January 28, with Hai Duong accounting for 611.