Myanmar has repatriated nearly 10,000 migrants from Malaysia this year, state media said on Monday, a day after a flotilla returning almost 1,500 of its citizens docked in the country.

The United Nations (UN) has sharply criticised Malaysia's push to return migrants to Myanmar under an opaque scheme it says cannot guarantee safe homecomings to the war-torn nation.

A group of 1,476 returnees arrived by ship outside Yangon on Sunday, the first of 5,000 that Kuala Lumpur says Myanmar agreed to take back amid a wave of anti-migrant sentiment in Malaysia.

Rights monitors have raised concerns that members of the Rohingya minority may be sent back to Myanmar, where they have faced violent persecution, but Malaysia has not commented on the ethnicities of returnees.

Myanmar revealed on Monday that a parallel and larger repatriation push has also been taking place by plane.

Between January and August this year, "8,041 citizens were repatriated by air", state newspaper The Global New Light of Myanmar said.

While the ship returns have been highly publicised in Malaysia, Kuala Lumpur has not commented on the returns Myanmar says it organised by weekly flights.

The total number of migrants Myanmar has said returned by plane and ship this year is 9,517.

Malaysia insists returnees under its scheme agreed to voluntary repatriation from detention centres, where Myanmar says they had "faced difficulties" after serving sentences for immigration offences.

But rights groups report dire conditions in the facilities, and the UN refugee agency says staff were not allowed to verify that decisions to return were "were genuinely free and informed".