A Metlink bus in Lower Hutt has crashed into a concrete fence on the wrong side of the street before catching fire, a witness says.
Emergency services were called to the crash on High Street at 8am.
Three people are being treated for injuries, and the Wellington Free Ambulance is transporting one person with moderate injuries to Wellington Hospital.
A police spokesperson said it was likely the bus driver suffered a medical event, causing the vehicle to swerve onto the wrong side of the road.
Gordon Wood, who runs a local butcher shop, told 1 NEWS that the bus caught fire for a brief amount of time.
"People were staggering from the back of the bus, trying to open the door," he said.
He said he’d never seen a crash this bad on High Street in the 21 years he’d worked there.
A Metlink spokesperson said the company was investigating the cause of the crash. The bus was on route 121.