A top UN official on Sunday urged Qatar to improve conditions for foreign labourers, as the Gulf emirate builds a massive infrastructure for the 2022 football World Cup.

"Many migrants face human rights violations in the workplace," said the UN special rapporteur on the human rights of migrants, Francois Crepeau, concluding an eight-day visit to Qatar, which has come under fire over the alleged exploitation of workers.

"Some are not paid their wages, or are paid less than agreed," he said.

"I am also concerned about the level of accidents in construction sites, and hazardous working conditions resulting in injury or death," he told a press conference.

Qatar has the highest ratio of migrants to citizens in the world. Approximately 88 per cent of the total population are foreign workers, he noted.

Crepeau urged the energy-rich state to introduce measures that would protect workers, including establishing a minimum wage for all employees, including domestic staff.

Gulf countries do not enforce a minimum wage for foreign workers, leaving it up to employers.

The UN envoy advised an "effective labour inspection system," with more inspectors "well trained on human rights standards, and interpreters in the most commonly used languages."

He also called for the "right of association and to self-organisation for all workers," in addition to allowing workers to change jobs "without sponsor/employer consent and (to) abolish the exit fee requirement."

The sponsor system, by which an employee must be sponsored by an individual or a firm, is applied in most Gulf countries, leaving expats at the mercy of sponsors who could refuse to allow them to leave.

Crepeau recommended that Qatar ratify a number of UN conventions on the protection of migrant workers, civil and political rights, and the convention against torture.

Britain's Guardian newspaper earlier this year charged that labourers in Qatar were faced with "modern-day slavery" and were paying with their lives.

The country has come under the spotlight of human rights organisations as it embarks on a multi-billion-dollar plan to host the 2022 World Cup.

Sepp Blatter, chief of world football's governing body FIFA, said on Saturday from Doha that the issue of working conditions in Qatar was being addressed.