A Mozambican court on Wednesday sentenced two ex-spy bosses and the son of a former president to 12 years each for their part in a corruption scandal in which the government sought to conceal huge debts, triggering financial havoc.

The former head of security and intelligence, Gregorio Leao; the head of the security service's economic intelligence division, Antonio do Rosario; and ex-president Armando Guebuza's son Ndambi Guebuza were among 19 defendants accused in the country's biggest graft scandal.

"The crimes committed have brought consequences whose effects will last for generations," said Judge Efigenio Baptista.

The scandal arose after state-owned companies in the impoverished country illicitly borrowed $2 billion (1.9 billion euros) in 2013 and 2014 from international banks to buy a tuna-fishing fleet and surveillance vessels.

The government masked the loans from parliament and the public.

When the "hidden debt" finally surfaced in 2016, the International Monetary Fund (IMF) and other donors cut off financial support, triggering a sovereign debt default and currency collapse.

An independent audit found $500 million of the loans had been diverted. The money remains unaccounted for.

Handing down the sentence following after a week of reading the verdicts, the judge said the scam "aggravated the impoverishment of thousands of Mozambicans."

"The country became famous for the worst reasons," he said.

Leao and do Rosario were found guilty of embezzlement and abuse of power, while Guebuza was convicted for embezzlement, money laundering and criminal association among other charges.