Moments before Los Angeles basketball great Kobe Bryant, his 13-year-old daughter and the seven others perished in a helicopter crash, the pilot had tried to climb out of layer of clouds, but the aircraft then banked sharply and lurched toward the ground.

The twin-engine Sikorsky S-76B slammed into a hillside 60 seconds later and burst into flames, killing all nine people on board, according to details of Sunday's crash revealed by U.S. federal aviation safety officials.

The death of Bryant, 41, an 18-time NBA all-star and one of the most admired athletes around the globe, sent shockwaves through the sports and entertainment worlds.

Investigators with the National Transportation Safety Board (NTSB) estimated Bryant's luxury passenger helicopter hit the ground at a speed of more than 2,000 feet (610 m) per minute.

"This is a pretty steep descent at high speed," NTSB board member Jennifer Homendy told a briefing in Calabasas, a town adjacent to the crash scene about 40 miles northwest of downtown Los Angeles.

"The time from descent to impact was probably about a minute."

Radar data showed that the helicopter had ascended to 2,300 feet - "he was trying to climb out of the cloud layer at the time" - and then began a left descending turn before air traffic control lost contact with it, Homendy said. 

Investigators have offered no explanation for what might have led the aircraft to bank abruptly to one side and then plummet to the ground. But Homendy said the estimated rate of descent "wouldn't be a normal landing speed."

"We know this was a higher-energy-impact crash," she said, adding that investigators had surmised that the helicopter was still in one piece before hitting the ground.

Homendy said that clouds, fog and limited visibility reported in the area on Sunday were a key focus of the investigation, which will take at least a year to complete.

The helicopter was not equipped with any kind of "terrain awareness and warning system," a device that might have alerted the pilot that the aircraft was dangerously close to the hillside, Homendy said. Nor did the chopper carry a "black box" flight data recorder, which would make it easier to piece together the cause of the crash, she said.

NTSB recommendations that both devices be required equipment on helicopters like the one that crashed on Sunday have not been implemented by the Federal Aviation Administration, she said.

Homendy briefed reporters as authorities completed the on-scene phase of the investigation, clearing the tall, grassy slope of remaining wreckage and human remains.

Among items recovered were an iPad that investigators hope may have belonged to the pilot for use in tracking flight and weather information, Homendy said.

The NTSB team carted a truckload of debris wrapped in large, white tarp bags while medical examiners positively identified remains of four victims, including Bryant and the pilot.

NTSB officials privately briefed relatives of the dead by telephone on Tuesday, but Homendy declined to say anything about what was discussed or who took part in the call.

Vanessa Bryant makes her first public statement on Instagram

Kobe Bryant's widow, Vanessa Bryant, made her first public statement on Wednesday, posting a long message on Instagram.

"My girls and I want to thank the millions of people who've shown support and love during this horrific time. Thank you for all the prayers. We definitely need them."

"We are completely devastated by the sudden loss of my adoring husband, Kobe - the amazing father of our children; and my beautiful, sweet Gianna - a loving, thoughtful, and wonderful daughter, and amazing sister to Natalia, Bianka, and Capri."

Vanessa went on by saying she and three other daughters are trying to make it because they felt that Kobe and Gianna are leading their way. 

"I'm not sure what our lives hold beyond today, and it's impossible to imagine life without them. But we wake up each day, trying to keep pushing because Kobe, and our baby girl, Gigi, are shining on us to light the way."

In her posting, Vanessa sent her condolences to the families who also lost their loved ones on Sunday and shared the news that MambaOnThree Fund has been set up to support the other families affected by the tragedy.

Earlier on Wednesday, Vanessa changed her Instagram profile photo to Kobe and Gianna. 

Separately, the Academy of Motion Picture Arts and Sciences said the February 9 Oscars ceremony would include a salute to Bryant.

NFL commissioner Roger Goodell also said on Wednesday during his annual pre-Super Bowl press conference that some form of tribute to Kobe Bryant is in the works for Sunday around the NFL's championship game.