Over 300 Mozambique nationals were in various South African jails for crimes of murder, theft and rape, the media reported.
According to the VOA Radio, the number had risen from 213 as at July 4 last year, as the Mozambique nationals were arrested on almost daily basis.
There were also reportedly 70 Mozambican nationals facing life terms over murder and rape crimes, the VOA added.
A vast border
The radio said further that Maputo authorities were investigating the allegations against the Mozambicans.
The Mozambican ambassador to South Africa, Mr Paulino Macaringue, was quoted as saying there was inadequate protection for immigrants in South Africa.
He disclosed that they had requested updated information on the Mozambique inmates in South Africa but the feedback was not forthcoming.
Mozambique and South Africa share a vast border and are important economic partners.
It is believed that over 2,000 Mozambican nationals live in South Africa where they mainly work in agriculture, mines and in the informal economy.
The two countries are members of the Southern African Development Community (SADC).
Other SADC member states are Angola, Botswana, Congo Brazzaville, Democratic Republic of Congo, Lesotho, Madagascar, Mauritius, Namibia, Seychelles, Swaziland (now eSwatini), Tanzania, Zambia and Zimbabwe.
South Africa is the largest economy and the most developed SADC state.