A hot-air balloon that crashed in the New South Wales Hunter Valley with 15 people onboard has left four people in hospital, including a young woman with suspected spinal injuries.

The balloon’s basket made a hard landing, tipped sideways and was dragged a number of metres at Greta, about 21km from Cessnock, on Saturday morning.

Balloon Safaris has blamed a quicker than expected shift in wind speed for the accident, saying conditions were calm in the morning when four hot-air balloons took off around 5.45am.

“The pilot decided to land at the first available landing spot,” a company spokesman said on Saturday. “The balloon landed firmly and some injuries were sustained by passengers in the basket as a result.”

Six people were injured, including a woman in her 20s with suspected spinal injuries and an 80-year-old woman who fractured her leg, a NSW Ambulance spokesman said.

They were both airlifted to the John Hunter Hospital by the Westpac Rescue Helicopter.

NSW Ambulance transported two other women, one with a suspected fractured rib and another with a cut to her head, to Maitland district hospital. All the women are in a stable condition.

The other two people only suffered minor cuts and didn’t require further treatment, a NSW Ambulance spokesman said.

A Balloon Safaris spokesman said the company regretted the incident and has been providing assistance and support to the passengers and their families.

The Air Transport Safety Bureau has been notified and is expected to investigate the incident.