Work has been going on for two weeks now to fix the road surface and is scheduled to finish by month-end.
It is carried out between 11 p.m. and 4 a.m. when only cars are allowed and traffic is light, and so commuters are not affected much, Doan Van Tan, director of the HCMC Urban Traffic Management Center, said.
But he admitted some parts are cordoned off by iron sheets during the day, forcing vehicles to slow down and cause congestion during rush hour.
The contractor had initially said the work would go on until January 9, but later promised to speed it up and complete it before the New Year.
The tunnel runs 1.49 km under the Saigon River and is a vital part of the city's east-west traffic flow. It is used by around 55,000 cars and 300,000 motorbikes every day.