Dr. Bandy Lee's stark alarm, published Friday in a letter to The New York Times , calls for the public and lawmakers to demand a psychological examination of Trump.

A Yale University psychiatrist is warning that President Donald Trump has become increasingly mentally unstable in recent days, imperiling the United States and the rest of the word.

Then presidential-candidate Donald Trump mocking a New York Times reporter during a rally in South Carolina in 2015.

Lee, the editor of the book "The Dangerous Case of Donald Trump: 27 Psychiatrists and Mental Health Experts Assess a President," said in her letter to the Times that "thousands" of mental health professionals are deeply worried about Trump's state of mind.

They have formed a group called the National Coalition of Concerned Mental Health Experts, whose website is Dangerouscase.org.

"All agree that he's dangerous," Lee told CNBC.

In her letter to the Times, Lee wrote: "We are currently witnessing more than his usual state of instability — in fact, a pattern of decompensation: increasing loss of touch with reality, marked signs of volatility and unpredictable behavior, and an attraction to violence as a means of coping."

"These characteristics place our country and the world at extreme risk of danger."

"Ordinarily, we carry out a routine process for treating people who are dangerous: containment, removal from access to weapons and an urgent evaluation," Lee wrote.

"We have been unable to do so because of Mr. Trump's status as president. But the power of the presidency and the type of arsenal he has access to should raise greater alarm, not less."

"We urge the public and the lawmakers of this country to push for an urgent evaluation of the president, for which we are in the process of developing a separate but independent expert panel, capable of meeting and carrying out all medical standards of care."