An inquest into the deaths of two teenage girls who died after similar falls at top-level equestrian events has heard that one of the girls was on the course with her mother for more than seven minutes before medical staff arrived.

Caitlyn Fischer, 19, was killed instantly when she was crushed by her horse, Ralphie, at a fall on jump two of the cross-country course at the Sydney international horse trials on 30 April 2016.

Just seven weeks earlier, on 6 March, Olivia Inglis, 17, died when she was crushed by her horse, Coriolanus, at a fall on jump eight at the cross-country course at Scone horse trials in the New South Wales Hunter Valley.

The deaths of the two riders, who were both experienced for their age and competed at the top of their field, sent shockwaves through the equestrian community in Australia and triggered a range of reforms including collapsable jumps on cross-country courses and improvements to medical care in competitions.

A two-week inquest began in Sydney on Monday and will look at whether the design of the course contributed to their deaths, whether safety procedures at NSW equestrian events are sufficient to minimise risk, and whether medical training and emergency response procedures at horse events are adequate.

The counsel assisting the coroner, Peggy Dwyer, told the court both young women were extremely competent riders with fit horses and appropriate safety gear.

Both competed in eventing, a three-stage competition in which riders complete a dressage test, a cross-country jumps course and a show-jumping course.

Fischer was competing at one-star level, the first level of international competition. She had owned the thoroughbred Ralphie for five years and had been living, working and training with her coach, Christine Bates.

On the morning of the cross-country event, Fischer told Bates that Ralphie was still “feeling a little strong” after their warm-up but she did not appear concerned.

Fischer’s mother, Ailsa Carr, was standing 50m from jump two when Fischer left the starting box at 10.40am. Dwyer said Ralphie made an “error with his striding” on the approach to jump two and jumped late, falling and crushing Fischer beneath him.

Carr, a trained nurse, ran to her daughter, identified that she had died, and called her husband, Fischer’s father, before anyone else arrived. Bates and the volunteer coordinator arrived next and began CPR, despite Carr asking them to stop. By the time medical staff arrived at 10.50am to confirm Fischer’s death, Carr had already called her husband again to arrange for him to fly to Sydney.

Inglis competed at two-star level, one rung below Olympic standard, and was the youngest member of the NSW state eventing squad.

She and nine-year-old ex-racehorse Coriolanus, who broke his neck in the fall that killed Inglis and had to be euthanised, had completed 13 one-star events without fault before progressing to two-star level.

The parents of Olivia Inglis, Arthur and Charlotte Inglis, arrive at the Lidcombe coroner’s court in Sydney. Photograph: Peter Rae/AAP

“Olivia had competed him at almost every cross-country course in NSW and his record was impeccable,” Dwyer said. “In over 28 starts together in the cross-country, Olivia and Coriolanus had only ever had one error.”

She and her mother, coach Charlotte Inglis, walked the cross-country course in Scone twice.

Dwyer said Charlotte Inglis remembered raising concerns about jump eight, a two-part jump where both fences had a downhill approach, and had discussed it with Olympian Shane Rose while her daughter was warming up. She told her daughter to retire from the course if Coriolanus did not take the earlier jumps well.

Inglis left the starting box at 9.11am. Two minutes later Coriolanus hit the second fence at jump eight, falling and causing fatal crush injuries to Inglis’s chest.

She was attended at the scene by paramedics, who arrived within one to three minutes, and an air ambulance, but she was declared dead at 10.05am.

The inquest continues.