Tens of thousands of children were sent abroad to former British colonies, including New Zealand (file pic).

An inquiry into historical child sex abuse and institutional failings by the British Empire has revealed details of migration schemes to New Zealand and other former colonies.

On Monday, the inquiry had its first day of public hearings and testimony from some of those who were abused while they were in care in Australia.

Thousands of children, many homeless, orphaned or in state institutions, were sent to former British colonies, mainly Canada, Australia, New Zealand, and Zimbabwe.

BEN PRUNCHNIE/ GETTY IMAGES New Zealand judge Justice Lowell Goddard resigned as chair of the UK inquiry in 2016.

The inquiry has been plagued by setbacks since it was announced in 2012, following the revelation the former BBC presenter Jimmy Savile was one of the United Kingdom's most prolific serial sex abusers.

In its first stage, the inquiry will hear public testimony from people who were sent to the colonies and abused.

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The policy, which covered institutions in England and Wales, encompassed World War II and was intended to reduce labour shortages.

The inquiry cannot bring prosecutions but can make findings of fact.

Child migration programme lead counsel Henrietta Hill QC said the scope of the overall inquiry was very broad and the child migration programme was one of the narrower case studies.

"In summary ... the child migration programmes were large-scale schemes in which thousands of children, many of them vulnerable, poor, abandoned, illegitimate or in the care of the state, were systematically and permanently migrated to remote parts of the British empire by various institutions in England and Wales, and with the knowledge and approval of British government.

"Many allegations of sexual abuse have been made by former child migrants."

Of the 100,000 children sent abroad, around 90,000 were sent to Canada between 1869 and 1924. Around 6900 child migrants were sent to Australia between 1913 to the early 1970s, and about 549 children were sent to New Zealand between 1949 and 1953.

Professor Stephen Constantine told the inquiry most child migrants were sent to institutions, but New Zealand's case was "curiously different" and involved an organisation called the Royal Overseas League, which organised for 549 child migrants to be sent into foster care in New Zealand between 1949 and 1953, and for children to be fostered in Australia.

Constantine said the colonies were interested in acquiring labour and increasing the white population, and the authorities at the time often repeated the phrase "good white British stock".

"This [fostering] requires children being authorised by law, through the magistrates' courts, so there is quite a close screening process that takes place that enables these children to be sent to New Zealand where they are under the guardianship of New Zealand government and its child welfare department and are then put supposedly into the safe hands of foster parents."

Most of the post-war child migrants were sent to Australia and, the inquiry heard, their families were often lied to before youngsters were sent abroad.

In some cases, parents tried to get their children back, while others were deported from England or Wales without their families' knowledge.

Sexual abuse was prevalent and the migrants were also expected to work long hours as "slave labour".

"The children were expected to work long hours and weekends making bricks for building projects, working as labourers in their bare feet, building cow sheds, shearing and killing sheep.

"Young boys worked in rock quarries in the baking heat of Australia."

The first three figures appointed to lead the investigations stepped down, the latest being New Zealand High Court Justice Lowell Goddard, who resigned last August. The following month, its most senior lawyer also quit.

The multimillion-pound inquiry's child migration programme case study runs for nine days until March 10.