A 47-year-old woman was taken to a hospital in serious condition Wednesday after a large tree branch fell on her on the main street in Waikiki.

At about noon Wednesday, witnesses said the woman, described as a visitor, was sitting on part of a concrete street planter under an autograph tree along Kalakaua Avenue when a large tree limb split off and fell on her. The branch, which was about 15 feet long, fell on the woman in two seconds.

This was fronting the Nani Aloha Shirt Outlet store near Kealohilani Avenue. A nearby lifeguard and police officer assisted the woman before paramedics arrived.

The Emergency Services Department said she was transported to a trauma center in serious condition.

In an emailed statement, Jon Hennington, spokesman for the Department of Parks and Recreation, said the Division of Urban Forestry staff is investigating the cause of the fallen limb.

"The initial inspection shows no clear point of failure, nor any signs of decay," he said. "The investigation will include a forensic examination of the branch by certified arborists."

A city crew cut down and removed the entire tree by 1:45 p.m.

Hennington said, "The autograph tree is one of the trees under DUF’s maintenance jurisdiction, and was last pruned by a city contractor March 30, 2015."

On June 25, a city crew removed a cracked branch hanging from the tree.

"An inspection of the tree at the time showed no signs indicating that further pruning was needed," he added.

Kana’i Sarkissian, a groundskeeper with the Department of Parks and Recreation, who was a few minutes away from the scene when the branch fell, said he believes the limb was top heavy due to thick foliage.

That, combined with the wind, caused it to split and fall, he said.

David Cox, a sales associate at the GNC vitamin and supplement store next to Nani Aloha Shirt, said there are strong winds from time to time.

While inside the store Wednesday, he heard the tree branch shear. The sound was sharp like "sheeooh," said Cox.

"There was no way to run away … It was too fast," he added.

In 2012, a California couple was injured when an 8-foot branch fell on them from a tree at the old International Marketplace.

The autograph tree, Clusia rosea, native to Florida and the Caribbean, was imported as an ornamental plant.

It gets its name from its leaves, which have a dark green outer layer and light green inner layer. People will scratch the leaf with something sharp, which removes the outerlayer, to write their name or messages, which last as long as the leaf stays on the tree.