African migrants in Israel begin hunger strike as thousands face imprisonment or deportation.

Hundreds of African migrants launched a hunger strike to protest Israel's implementation of its controversial policy to expel or indefinitely imprison them, a spokesman for the group said Wednesday.

Israel has resolved to expel thousands of Eritreans and Sudanese who entered illegally over the years, giving them an ultimatum to leave or risk being imprisoned indefinitely.

As the migrants could face danger or imprisonment if returned to their homelands, Israel is offering to relocate them to an unnamed third country, which the migrants and aid workers say is Rwanda or Uganda.

Authorities on Tuesday transferred seven Africans from the Holot detention centre to a nearby prison, prompting the 750 men held in Holot to launch a hunger strike that evening, said Abdat Ishmael, an Eritrean held at the southern Israel open facility.

On Wednesday, another five were taken to prison, Ishmael told AFP.

A spokeswoman for the Israeli interior ministry confirmed they had begun implementing the deportation or prison policy on Holot detainees ahead of the April 1 mark for the rest of the Africans who had entered Israeli illegally.

Ishmael said they would prefer prison over deportation to Africa.

"We saw what happened to people who went (to other African countries) a year or two ago, they don't receive asylum and can die," he said.

Migrants began entering Israel through what was then a porous Egyptian border in 2007. The border has since been strengthened, all but ending illegal crossings.

Israel's deportation or imprisonment plan has drawn criticism from the United Nations' refugee agency as well as some in Israel.

According to interior ministry figures, there are currently some 42,000 African migrants in Israel, half of them children, women or men with families, who are not facing the April deportation deadline.

Israeli officials stress that no one they classify as a refugee or asylum seeker will be deported.