According to the mayor of Arusha, Gaudence Lyimo, the city-owned gravel pit had already witnessed several fatal incidents.
The latest followed the collapse on Friday of a 16-storey building in Tanzania's commercial capital Dar es Salaam that left at least 25 dead, according to local media.
The owner of the building was arrested for violating a construction contract that had authorised a 10-storey structure, while three people responsible for contracting and quality control were being held by police for questioning
Authorities ordered the demolition of three adjacent buildings that were damaged.
President Jakaya Kikwete, after a visit to the site, warned of legal action against those responsible for the "negligence".
Local and international rescue workers and security forces took part in the search for survivors.
