Hundreds of thousands of Nepali migrants working in Gulf states must be allowed to return home after a massive earthquake devastated their impoverished nation, a trade union group said.

The International Trade Union Confederation (ITUC), which has 176 million members globally, said it had written to the Qatar, Saudi Arabia and UAE governments to ask them to suspend a sponsorship system which prevents the free movement of workers.

"We call upon the Gulf states, which rely so heavily on cheap and exploited labour from Nepal, to show compassion and immediately suspend the kafala restrictions which are stopping Nepalese people returning home for bereavement and to help reconstruct the country," said ITUC general secretary Sharan Burrow in a statement.

Nepal's Prime Minister Sushil Koirala told Reuters on Monday that the death toll from Saturday's earthquake could reach 10,000.

Hundreds of thousands of people in the Kathmandu Valley, which includes the capital city, are in desperate need of food, clean drinking water and shelter. The United Nations estimates up to 8 million people have been affected by the quake.

Thousands of Nepalis migrate to countries in the Middle East, India and Malaysia every year due to poverty and a lack of jobs. Many work on construction sites or as domestic staff.

Nepal, one of the world's poorest countries, is heavily reliant on remittances. The money workers send back has nearly doubled in the last two years to $4.34 billion -- more than 20 per cent of Nepal's gross domestic product.

In February 2014, the Guardian newspaper reported that more than 400 Nepali workers had died building football stadia in Qatar for the 2022 World Cup. Both governments dispute the figures.

Under international pressure to improve conditions for migrant workers, Qatar said in November it would introduce new labour legislation by early 2015, but this has not happened yet.

The Brussels-based ITUC called on Gulf states to ensure that exit permits and other restrictions are waived for Nepali workers who want to return home and that payment of salaries continue for workers on bereavement leave.

Those who wish to leave permanently must be allowed to do so with end-of-service benefits, it added.  - Reuters