Nguyen Manh Hung is being investigated for flouting provisions of the laws on investment in construction leading to serious consequences, Major General To An Xo, the spokesman for the Ministry of Public Security, said.

Six others, including employees of the corporation, the country's biggest highway builder, and members of the project management board have been placed under house arrest on the same charges.

Xo said the seven are accused of violating construction regulations during the construction of the expressway, final checks and takeover.

Hung was acting general director of the Railway Project Management Unit before taking over at Vietnam Expressway Corporation (VEC).

The Ministry of Public Security has launched criminal investigation against 20 people since November last year for violations related to the project, including Le Quang Hao, deputy general director of VEC, and Nguyen Tien Thanh, former director of the project management board.

The VND34.5-trillion ($1.4 billion) expressway opened to traffic in September 2018.

But just a month later it developed cracks and potholes meters wide and 5-10 centimeters deep after a heavy downpour.