Over 31 million people – one person every second, every day of the year – were uprooted in their home country in 2016 because of conflicts and disasters.
The number will grow unless the underlying causes such as political turmoil and climate change are tackled, an international aid group said on Monday.
Unlike refugees, who seek asylum in other countries, internally displaced people (IDPs) remain in their own country and cannot claim international protection, according to the report, by the Internal Displacement Monitoring Centre (IDMC).
For this reason, IDPs are often overlooked until humanitarian crises spill across borders, said IDMC's director Alexandra Bilak.
Nearly 7 million people, mostly from sub-Saharan Africa and the Middle East, were displaced because of conflicts, according to the data by IDMC, which is part of the aid agency Norwegian Refugee Council (NRC).
A further 24 million people, mainly in Asia, were forced to flee to another area of the country due to natural disasters such as storms, floods and wildfires, IDMC said.
Jan Egeland, the head of the NRC, said the figures show the need to focus as much on people displaced inside their countries as on refugees who flee across borders.
"Internally displaced people now outnumber refugees by two to one. It is urgent to put internal displacement back on the global agenda," said Egeland.
In 2016, conflicts uprooted the most people in the Democratic Republic of Congo, with 922,000 fleeing their homes, followed by Syria (824,000) and Iraq (659,000).
But natural disasters displaced three times as many people as conflicts, with more than 7 million people in China forced to leave their homes, followed by the Philippines at nearly 6 million and India at nearly two-and-a-half million.
Afghanistan ranked fourth in terms of displacement caused by conflict, with 653,000, followed by Nigeria with 501,000 and Yemen with 478,000.
Serious policymaking urged
Bilak said policymakers urgently need to address the root causes of displacement and focus more attention on IDPs since they may well flee to other countries if their situation worsens.
Millions of Syrians were displaced during the first years of the war, Bilak said, and it wasn't until 2014 and 2015 when they started to flee the country in huge numbers, triggering the biggest migration crisis since World World II.