The plight of hundreds of thousands of Rohingya people is said to be the world's fastest growing refugee crisis.
Risking death by sea or on foot, more than half a million have fled the destruction of their homes and persecution in the northern Rakhine province of Myanmar (Burma) for neighbouring Bangladesh since August 2017.
The United Nations described the military offensive in Rakhine, which provoked the exodus, as a "textbook example of ethnic cleansing".
Myanmar's military says it is fighting Rohingya militants and denies targeting civilians.
Who are the Rohingya?
The Rohingya, who numbered around one million at the start of the year, are one of Myanmar's many ethnic minorities. Rohingya Muslims represent the largest percentage of Muslims in Myanmar, with the majority living in Rakhine State.
They have their own language and culture and say they are descendants of Arab traders and other groups who have been in the region for generations.
But the government of Myanmar, a predominantly Buddhist country, denies the Rohingya citizenship and even excluded them form the 2014 census, refusing to recognise them as a people.
It sees them as illegal immigrants from Bangladesh.They have been described as among the world's "least wanted" and "most persecuted" minorities.
Since the 1970s, Rohingya have migrated across the region in significant numbers. Estimates of their numbers are often much higher than official figures.
In the last few years, before the latest crisis, thousands of Rohingya were making perilous journeys out of Myanmar to escape communal violence or alleged abuses by the security forces.
Why are they fleeing?
The latest exodus began on 25 August after Rohingya Arsa militants attacked more than 30 police posts.
Refugees arriving in an area known as Cox's Bazaar - a district in Bangladesh - say they fled after troops, backed by local Buddhist mobs, responded by burning their villages and attacking and killing civilians.
Amnesty International says the Myanmar military has killed hundreds of Rohingya and raped and abused Rohingya women and girls.
The government claims that "clearance operations" against the militants ended on 5 September, but BBC correspondents have seen evidence that they continued after that date.
At least 288 villages were partially or totally destroyed by fire in northern Rakhine State in Burma after August 2017, according to analysis of satellite imagery by Human Rights Watch.
The imagery shows many areas where Rohingya villages were reduced to smouldering rubble, while nearby ethnic Rakhine villages were left intact.
Human Rights Watch say most damage occurred in Maungdaw Township, between 25 August and 25 September - with many villages destroyed after 5 September, when Myanmar's de facto leader, Aung San Suu Kyi, said security force operations had ended.
What is the scale of the crisis?
The UN says the Rohingya's situation is the "world's fastest growing refugee crisis".
Before August, there were already around 307,500 Rohingya refugees living in camps, makeshift settlements and with host communities. according to the UNHCR.
Most Rohingya refugees reaching Bangladesh - men, women and children with barely any belongings - have sought shelter in these areas, setting up camp wherever possible in the difficult terrain and with little access to aid, safe drinking water, food, shelter or healthcare.
Of the 537,000 refugees who have arrived since August 58% are are children, while 60% of the adults are women.
The largest refugee camp is Kutupalong but limited space means spontaneous settlements have sprung up in the surrounding countryside and nearby Balukhali as refugees keep arriving.
While the Kutupalong refugee camp has grown from 13,901 to 20,000 since August, the number living in makeshift or spontaneous settlements outside the camp has climbed from 99,495 to 311,225.
Other sites in the region have also expanded - as of mid-October 2017, there were 14 sites occupied by more than 10,000 people.
There are also around 145,651 people staying outside the camps in host communities.
Why is being done by international community?
The need for aid is overwhelming.
720,000 children in need of humanitarian assistance, according to Unicef
$434m in funding needed for UN humanitarian response plans over the next six months
900,000 doses of cholera vaccine mobilised for immunisation campaign
10,000 latrines to be built by Bangladesh military to provide sanitation for 250,000 people
500 tonnes of aid has been delivered in five airlifts
There has been widespread condemnation of the Myanmar government's actions but talk of sanctions has been more muted:
The UN Security Council appealed to Myanmar to stop the violence but no sanctions have been imposed
The US urged Myanmar's troops to "respect the rule of law, stop the violence and end the displacement of civilians from all communities"
China says the international community "should support the efforts of Myanmar in safeguarding the stability of its national development"
Bangladesh plans to build more shelters in the Cox's Bazaar area but also wants to limit their travel to allocated areas
Myanmar urged displaced people to find refuge in temporary camps set up in Rakhine state but hadded that Myanmar would not be able to allow all those who fled to Bangladesh to return
The UK Disasters Emergency Committee launched an appeal for funds to help the refugees and their overstretched host communities. UK Prime Minister Theresa May also said the military action in Rakhine had to stop. The UK has suspended training courses for the Myanmar military