Britney Spears says people should "find a new family" if they haven't "honoured you".

The 43-year-old star has shared a cryptic message about the important of family and protecting "your heart" above all else, as she shared a photo of the bottom of the ocean.

She wrote on Instagram: "Honor thy mother and father, but always protect your heart.

"Only honor them if they have sacredly honored you !!! If not, you find a new family."

The Toxic hitmaker didn't offer any context for her message, nor did she name any of her own family members.

The post came hours after her ex-husband Kevin Federline - with whom she has sons Sean Preston, 20, and Jayden James, 19 - expressed his concern over her "situation" and a fear that "something bad" is going to happen to her.

In an excerpt from his memoir You Thought You Knew shared by the New York Times newspaper, he wrote: "The truth is, this situation with Britney feels like it's racing toward something irreversible.

"It's become impossible to pretend everything's OK.

"From where I sit, the clock is ticking, and we're getting close to the 11th hour. Something bad is going to happen if things don't change, and my biggest fear is that our sons will be left holding the pieces."

Kevin went on to express his concern that the Free Britney movement - which campaigned to have his ex-wife's conservatorship terminated - may have "started from a good place" but has now left professionals who could help the Gimme More hitmaker afraid to step in.

While Kevin doesn't know the perfect "solution", he appealed for anyone "who has ever been moved by Britney" to stand by his children and their mother.

He wrote: "Now, more than ever, they need your support. I've been their buffer for years, but now it's bigger than me. It's time to sound the alarm."