Up to 50,000 Burundian refugees are stranded in an overcrowded lakeside village on the border with Tanzania, as aid agencies warn of mounting tension with local people and fear of disease.
The UN refugee agency said on Friday that more than 105,000 people have fled to neighbouring countries to escape political violence in Burundi.
Refugees have arrived in Tanzania, with most currently gathering at the Kagunga reception area where they are slowly being transported to the camp.
Aid agencies are preparing for the regional crisis to worsen following an attempted coup in Burundi. It is the worst violence to hit the small central African nation since its 12-year civil war ended in 2005.
Roadblocks and the closure of borders have been making it hard for people to flee, agencies said, as protests erupted over President Pierre Nkurunziza's plan to run for a third term.
"The reason there are so many people here is because we didn't feel secure back at home, because Imbonerakure (government youth militia) were going around and threatening people, saying they were going to finish them. This went on for a while. People were terrified, and they were wondering what they meant when they said 'we will finish them!' And then things got worse because we heard about what was happening in the capital," said one refugee who did not want to be named.
"This is the third time we have been forced to become refugees, and we will not go back to Burundi. During the last conflict, we were forced to flee into Tanzania, and Tanzania welcomed us, and treated us well. But we were later forced to repatriate back home, without much. When we arrived back to our country, no one helped us," added Focace, another Burundian refugee.
There's only one 100-year-old German boat transporting 1,200 refugees a day from Kagunga village to the Tanzanian port of Kigoma and it cannot keep up with the 2,000 daily arrivals.
Most of the refugees at Kagunga are women and children who have been sleeping out in the rain, according to UNHCR officials.
They are squeezed into a confined space with a shortage of toilets and drinking water in a village that is normally home to 12,000 people.
There are 26,000 refugees in Rwanda, 17,000 in Nyarugusu refugee camp further inland in Tanzania, and more than 7,000 in the Democratic Republic of Congo, the UNHCR said.
The ruling CNDD-FDD party denies charges its youth wing is armed and trying to stir violence.