Tens of thousands of people in southern Afghanistan have fled their homes following days of heavy fighting between the Taliban and security forces, officials said Wednesday, as violence continues to soar despite ongoing peace talks.

Taliban militants launched a series of attacks on the city of Lashkar Gah in restive Helmand province on Sunday night, prompting the US to call in airstrikes to defend Afghan forces. The fighting triggered an exodus by local residents who crammed onto motorcycles, taxis and buses.

"More than 5,100 families or 30,000 people... have fled the fighting so far," Sayed Mohammad Ramin, director of the refugees department in Helmand, told AFP. "Some families are still living in the open in the streets in Lashkar Gah, we don't have tents to give them."

Local resident Hekmatullah said he was forced to flee after a mortar hit his neighbour's house, killing two women. "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.

Fighting was ongoing in at least four districts on Wednesday, Afghan officials said, adding that security forces have repelled repeated Taliban assaults in the area.

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, inc. safe paths for those wishing to leave" the area.

A collision between two helicopters early on Wednesday in Helmand's Nawa district also killed at least nine people, according to Omar Zhwak, a spokesperson for the provincial governor. The defence ministry said they were investigating the incident.

Helmand -- a Taliban stronghold -- is where international forces fought some of the bloodiest campaigns of Afghanistan's 19-year war. Under a deal the Taliban signed with Washington in February, the insurgents are not supposed to hit urban areas and are meant to keep violence down.

The US committed to pulling all foreign troops from the country by next May in return for Taliban security pledges and an agreement to begin peace talks with the Afghan government in Qatar.

Talks began last month between the Taliban and Afghan government in Doha but appear to be stalled as the two sides have struggled to establish a basic framework for negotiations.