Two military helicopters evacuating wounded soldiers from fighting in southern Afghanistan collided on Wednesday killing nine people on board, the government said.
The crash happened as the helicopters were taking off in restive Helmand province, where clashes have erupted between Afghan forces and the Taliban, said provincial governor's spokesman Omar Zawak.
Afghanistan's defence ministry said the collision was due to "technical issues".
The incident followed heavy fighting in provincial capital Lashkar Gah, where Taliban militants launched a series of attacks on Sunday in an attempt to capture the city.
It prompted US forces to call in air strikes in an effort to defend Afghan troops.
The clashes have triggered an exodus of 30,000 people, said Sayed Mohammad Ramin, director of the Helmand province refugees department.
"Some families are still living in the open in the streets in Lashkar Gah, we don't have tents to give them," he told AFP.
Those fleeing crammed onto motorcycles, their belongings strapped on behind them, or into overcrowded taxis and buses.
"The fighting was so intense that I did not have time to take any extra clothes. I only took my family," said Attaullah Afghan, a farmer who fled with his family of 12.
Local resident Hekmatullah told AFP he was forced to flee after a mortar hit his neighbour's house, killing two women.
"I just want some peace to be able to live happily with my children and do my job as a farmer," said another man from the city.
Afghan forces had repelled the attempted takeover of the city and the security situation would "return to normal soon", said a defence ministry statement on Wednesday.
The United Nations Assistance Mission in Afghanistan said thousands had fled and called on Taliban fighters and security forces "to take all feasible measures to protect civilians" and allow safe passage for those hoping to leave the area.
Helmand -- a Taliban stronghold -- is where international forces fought some of the bloodiest campaigns of Afghanistan's 19-year war.
The insurgents pledged to keep violence down and avoid targeting urban areas in a February deal signed with Washington in February.
They also agreed to begin peace talks with the Afghan government, in return for a US vow to pull all foreign troops from the country by next May.
Those talks began last month in Qatar but appear to be stalled as the Taliban and the Kabul administration have struggled to establish a basic framework for negotiations.