Technology executive Adam Robinson, his wife, and their two children were among nine people killed when the business jet they were travelling in crashed in the US state of Florida on Sunday, their relatives have confirmed.

The Learjet 60 aircraft they were on board was seen slamming into the ground and exploding next to a road in Palm Beach County, in videos posted to social media.

Robinson was the co-founder and CEO of Retention.com, a marketing software company based in Austin, Texas.

He was originally a credit trader at Lehman Brothers and Barclay's Capital, according to his LinkedIn page, before becoming an investor and a co-founder of email marketing firm Robly.

Robinson's brother Anthony, who is CEO of supply chain technology company ShipScience, said he is "completely devastated" by the incident.

"My brother and his young family brought so much light to my life, to my family, and to countless others," he wrote.

"They were all robbed of a very bright future, and everyone else was robbed of more time with these incredible people."

Retention.com said it is "heartbroken" by the loss of Adam Robinson and his family.

"Adam was much more than our CEO," the company said in a statement.

"He was a friend, a mentor and a bold, outspoken leader who lived life to the fullest.

"He cared deeply about the people around him and brought energy and conviction to everything he built.

"His loss is deeply felt across our team and the tech community, as we collectively mourn this significant loss."

Robinson's wife, Helen Sharp, was a ceramicist and the CEO of her own public relations firm Influential PR at the time of her death.

Family's nanny and friends also killed

"Adam and Helen were devoted parents, and Emma, four, and Charlie, two, were the light of their lives," the affected families said in a joint statement.

"Helen and Adam were the love affair that will last forever.

"Their warmth, generosity and gift for making people feel welcome touched so many lives.

"Their loss will be felt deeply by all those who loved them and who they loved in return."

Also among those killed was the family's nanny, Anita Maria Cetina.

"Anita Maria cared for Emma and Charlie with tenderness and devotion, and she was truly part of the family," the statement read.

"She showed us a legacy of unconditional love and devotion."

The others killed in the plane crash were reported as family friends Rachael Reed and Charmi Fehr, and two crew members.

"We are deeply grateful to the first responders, investigators, and the Palm Beach County community for their care, and to everyone who has reached out with love," the families said.

"Our hearts are also with the families of the pilots, who are grieving alongside us."

Investigation into crash begins

The plane had taken off from Austin-Bergstrom International Airport in Texas and was travelling to North Eleuthera Airport in the Bahamas.

Since the crash, investigators have found evidence that the plane had begun to break up while in the air, National Transportation Safety Board member Tom Chapman told a news conference on Monday, US time.

In a second media briefing on Tuesday, Chapman said investigators had found the majority of the plane's left elevator – a key control surface on its tail – which had broken into three pieces and been scattered at least 2 kilometres from the crash site.

"The distance from the site indicates that it separated before impact," he said.

The "very significant piece of evidence" is being analysed to see if it contributed to the crash, he added.

Authorities also have "a lot of work" ahead to recover parts of the plane from the crater it left in the ground, including the cockpit voice recorder, Chapman said.

Weather will also be a major part of the investigation, as the pilots allegedly reported ice and turbulence before the jet's rapid descent.