A mother whose friend was killed by a falling branch at Kew Gardens during her three year old's birthday party has relived the tragedy at an inquest.

Erena Wilson, 31, from Hanwell, west London, was strolling through the Royal Botanical Gardens in September 2012 when she died.

It was only pure "fluke" that her friend Tess Marshall's daughter Ruby was not also killed as she had run ahead minutes before, John McLinden QC, the Wilson family's lawyer, told the inquest at West London Coroner's Court.

Mr McLinden said it had been raining heavily in the hours leading up to the accident on September 23. Tree branches are vulnerable to dropping off suddenly when they endure long dry spells followed by heavy rain - a condition known as 'summer branch drop', the court heard.

But Kew Gardens failed to put up signs warning of the danger because it deemed the risk to be so minimal, Mr McLinden said.

Ms Wilson was walking along a main path when Ms Marshall suddenly noticed a large Cedar of Lebanon branch, 20ft long and 12 inches thick, was crashing down from 20 yards above.

Ms Marshall screamed 'run' and fled for her life, but when she looked back she saw Ms Wilson, an accounts manager, lying sprawled on her front on the ground surrounded by debris from the tree.

Her voice dipping low as she recounted the tragedy, Ms Marshall said: "We were chatting and then, all of a sudden, I hear this crack like a lightning crack.

"I look to my left and saw the scar of a break in the tree so you could see the white colour underneath from a branch that had just broken off right at the very top of the tree.

"There was a whole load of foliage, branches and stuff just falling above my head.

"It blocked out the sky and all I could see was this umbrella of branches.

"As I was running, I thought the whole tree was falling over. I was sure it was going to hit me. I was running away and then I heard a heavy thud. An oomph."

She added: "I wasn't thinking, it was just instinct. I was just running."

She span around and saw her friend lying totally still on her front with blood coming out of her ears and mouth, forming a pool of blood under her face.

The branch fell with such force that it brought two others down in its wake and smashed Ms Wilson's backpack, making "sawdust" of the glass inside.

Ms Marshall said: "Because they had stopped and seen everything my three-year-old was really upset and crying so she went on with her auntie."

Ms Marshall's brother, who had been walking ahead with her daughter and his wife, dashed back and gave CPR until paramedics and an air ambulance arrived.

But Ms Wilson suffered severe head injuries, including fractures, bruising on her left side and scalp and an extensive brain injury. S he was pronounced dead at 2.51pm - after 45 minutes of cardiac resuscitation.

A post mortem found she died from "multiple injuries".

Ms Wilson, who was originally from Wellington, New Zealand, had arrived at Kew at around 1.45pm and was walking with Ms Marshall while Ms Marshall's brother and sister-in-law strolled ahead. Just minutes before the branch fell, Ruby dashed ahead and "ran free" with her uncle.

Addressing Ms Marshall, Mr McLinden said: "It was just a matter of chance that your daughter had run out of harm's way prior to this.

"It was just a fluke that the three of you weren't badly injured or worse by what happened."

Ms Marshall replied: "Yes absolutely. - guess it was a matter of chance. We were lucky."