The Dunedin City Council said the hole was protected by a cone, but it had been removed and had now been replaced by a more solid structure.
After falling, the woman was forced to wait on the ground on the main street for about an hour for an ambulance.
The woman was walking along the footpath in George St towards the Octagon in the Meridian block about noon when she slipped and injured her leg.
Her leg got stuck in a tree bed, which was lined with grates. There was no tree in the bed.
A person, who declined to give their name, said there was no protection around the hole.
"There should have been some cones around it and maybe some signs to say there was a danger there," the person said. "What they had was not adequate."
Once the ambulance had taken the woman away, the person grabbed a couple of nearby road cones to place around the hole so no-one else would be hurt.
The person said the cones he placed had disappeared yesterday.
St John said it was notified at noon on Saturday of a fall in George St. One ambulance and one rapid response unit responded.
A Dunedin City Council spokesperson said the council extended its sincere apologies to the woman.
"The tree in question was removed after being vandalised, and a cone placed at the site since appears to have been stolen or moved," the spokesman said.
"We have asked our contractor to replace the cone with a solid barrier as soon as possible, and this will remain in place until a new tree is installed."
