Geneva (AFP) - Nearly 127,000 Burundians have registered as refugees in neighbouring countries and many more have likely fled under the radar from the troubled central African nation, the United Nations said Friday.

Since Burundi's political turmoil started in April, the UN refugee agency said it had seen 62,000 Burundians register as refugees in neighbouring Tanzania, 45,000 in Rwanda, 10,590 in the Democratic Republic of Congo, 8,855 in Uganda and 400 in Zambia.

"Many more Burundians are thought to have left the country but have not registered as refugees," UNHCR spokesman Adrian Edwards told reporters in Geneva.

The exodus has come as around 70 people have been killed in weeks of brutally suppressed street protests.

The central African nation was plunged into turmoil in late April when President Pierre Nkurunziza launched his drive to serve a third consecutive five-year term.

Opponents say his third-term bid is unconstitutional and a violation of a peace deal that ended 13 years of civil war in 2006.

Opposition groups say they will boycott both parliamentary elections, due to be held on Monday, and the presidential vote on July 15.

Several top officials -- including the deputy vice-president, members of the election commission and constitutional court -- as well as numerous journalists and activists are among those who have fled poverty-stricken and landlocked Burundi.

Edwards said refugees were arriving in Tanzania at a rate of between 200 to 300 per day, and were being transferred to the overcrowded Nyarugusu refugee camp, which before the recent influx was already home to more than 60,000 Congolese refugees.

It is now hosting 120,000 refugees and UNHCR is working with the Tanzanian government to urgently identify an alternative site for a new camp, he said.

In Rwanda, the number of arrivals has meanwhile increased sharply in recent days, with more than 600 refugees flooding across the border each day, Edwards said.

A month ago, UNHCR and its partners appealed for $207 million to help protect and help up to 200,000 Burundian refugees, but have so far received just 13 percent of that amount.

"This leave crucial activities such as shelter, water, health, sanitation and education seriously underfunded," Edwards warned.