ALEPPO, Syria: Ambulance driver Abu Bakr tore down the road in the wrong lane, dodging oncoming cars in his bright yellow vehicle as he responded to yet another call in war-torn Aleppo, Syria's second city.

"We work 24 hours seven days a week. The war never stops and we don't either," he said, stopping near a minibus engulfed in flames.

"Mortar fire hit it, killing the three people inside, and a piece of shrapnel injured a woman passer-by who'd been food shopping," a rebel at the scene said.

The dead had already been taken away in cars or taxis.

A shoe and a sack of potatoes belonging to the wounded woman lay next to a pool of blood on the pavement.

Abu Bakr returned to the accident and emergency centre, parking inside an abandoned supermarket used to conceal a fleet of 16 ambulances, just 10 of which are in working order, that are driven by 22 staff.

Over the walkie-talkie he learned that the woman had lost a leg and was being transferred to Turkey for further treatment.

"It's impossible to see anything positive in life when you see this every day," he said. "But I like what I do because I'm helping people and I feel useful.

"Some people are good at fighting, but I'm behind the wheel saving lives."

Floodlights illuminated the parking area. Abu Mohammed, a colleague, got out of his ambulance with a sober look, having just returned from Zarzur hospital.

"I'm going to clean the ambulance," he said. The floor and stretcher inside were covered in blood.

His last run was with a man hit by mortar fire. He had "arrived at the hospital still alive but I'm not sure they can do much for him," Abu Mohammed said, hosing down the vehicle.

"Often when we clean out the ambulances we find pieces of people."

Sam Eddin, 32, coordinates the ambulance service from a small office, fielding calls from "hospitals, civilians and rebels fighting on the front."

Six weeks ago regime forces captured one of the vehicles at Aleppo airport as it waited to transport wounded insurgents.

"We still don't know if the driver is alive," said Eddin.

"If we try to cross a regime checkpoint to take the injured from one town to another, they confiscate the ambulance and arrest us. That's why taxis have to be used to take the wounded to hospitals in areas under regime control."

A voice crackled through on Abu Bakr's radio and he started his engine and turned on his siren to go and pick up a four-year-old girl wounded in by a mortar barrage.

The girl was wrapped in a blanket, her head bandaged and face covered in small cuts from shrapnel. Her distressed father sat next to her in the ambulance, along with a medic.

"We'll have to take her to Turkey. Doctors here can't do anything for her," Abu Bakr said.

The ambulances take around a dozen people a day over the border.

Abu Bakr stopped at a railway station, and the paramedic got out to talk to Turkish border guards.

"Many people we bring to the border don't have passports and can't cross legally, so we go to crossings where we know the Turkish soldiers will let them in for treatment," Abu Bakr said.

After a friendly exchange with the soldiers, the paramedic picked up the little girl and walked her through the barbed wire checkpoint to meet a Turkish army officer.

"We call an ambulance to take the injured to the nearest hospital. If they're not seriously hurt they then come back through the same crossing," the officer said, asking not to be identified.

"If the Syrian regime finds out, they'll try and block the route or destroy the road."

After Abu Bakr returned to Aleppo, another emergency call came in. A rocket hit in Saif al-Dawla had killed a dozen people and wounded 50. He sped off once again to help save lives.