A New Zealand court on Thursday found a man guilty of exploiting Fijian workers in the country's first human-trafficking conviction.

The case brought to light the darker side of New Zealand's immigration boom and represented a shift in focus by authorities who have been criticised for not taking a hard enough line on exploitation of migrants.

Faroz Ali, a 46-year-old Fijian citizen with New Zealand residency, was found guilty of people trafficking offences after promising 15 Fijian workers well-paid jobs in New Zealand, according to the Ministry of Business, Innovation and Employment, which investigates immigration offences.

The workers paid NZ$4,000 ($2,900) to Ali in ‘administration fees’ and were told they would earn up to NZ$900 a week to pick fruit.

Instead, they only got one-month visitor visas and low wages.

Ali made more than NZ$100,000 from the scheme, the ministry said.

‘It is the first conviction of that type in New Zealand,’ said Pete Devoy, an assistant general manager of border operations at the ministry, who led the team that investigated the case.

Record immigration numbers and a shortage of workers in the low-wage agriculture and horticulture sectors have raised the risk of immigrants being exploited, activists say.

‘It is definitely going on but to actually convert it from anecdotal evidence into something substantive to actually take to trial or prosecute is really difficult,’ said Peter Mihaere, chief executive of anti-people trafficking organisation Stand Against Slavery.

The US State Department said in its annual report on human trafficking that New Zealand needs to do more to get high-level criminal convictions.

The maximum sentence for people trafficking in New Zealand is 20 years in prison and a fine of up to NZ$500,000. Ali is scheduled to be sentenced in October.