MINGORA (Agencies) - Taliban militants blocked roads with rocks and trees, preventing terrified civilians from fleeing Swat Valley Thursday as the army stepped up a ground and air assault on the guerrillas that has been applauded by the US, witnesses said. More than 500,000 people driven out by fighting in other regions of the northwest are already living in makeshift camps or with relatives, adding a growing humanitarian crisis to the countrys daunting security, economic and political problems. With Taliban militants roaming the streets of Mingora, Swats main town, on Thursday and troops launching artillery and airstrikes on militant targets from helicopter, many residents hunkered down in their homes. The Army announced it was relaxing its blanket curfew in the area, but some of those who tried to make a swift exit said militants blocked their way. Ayaz Khan, a 39-year-old from the Kanju area of Swat, said he loaded his family into his car early Thursday but that rocks, boulders and tree trunks had been laid across the roads, forcing him to turn back. I am helpless, frustrated and worried for my family, he told a foreign news agency by telephone from his home. He appealed to authorities to clear the barriers and let people move to safety. A health worker living in Mingora said militants had warned her to stay in her home. During the whole of last night, I heard firing, and again this morning, said the woman, who would only give her first name, Maryam, for fear she could be targeted for speaking with a reporter. I dont know when some weapon will hit our home and kill us, she said. Aid workers warned that the humanitarian crisis was escalating in the area after families streamed out of the Taliban militant stronghold on foot or crammed into cars weighed down with provisions and household possessions. A mortar shell hit the outer wall of my house last night. Luckily, we survived. I feel God has given me an opportunity I cant miss. Im leaving. Swat is not worth living in, Nasir Jamal, a medical shop owner, told AFP. We cant stay here when bombs are falling all around, said resident Mohammad Hayat Khan as he loaded his family of 14 onto a pick-up truck. He said there had been shelling near his home. People began fleeing Mingora when authorities temporarily lifted a curfew. Swats top administrator, Khushal Khan, said people were not being advised to leave but authorities were helping those who wanted to go. There are troop convoys coming and once that is over, public transport will be able come into the town. In the meantime, we are extending whatever help possible to people leaving, he said. Many displaced stay with friends, relatives and in rented accommodation but the exodus puts an extra burden on an economy propped up by a $7.6 billion International Monetary Fund loan. Residents said they were suffering from both the military bombardment by government forces and the guerrilla tactics of the Taliban, who have terrorised the population in Swat by kidnapping and killing those who oppose them. Civilians are suffering at the hands of both the army and the Taliban. The Taliban are killing residents who dont side with them, said the shop owner Jamal.