The phrase "a highly alarming" is correct and usable in written English.
It can be used to describe something that causes a significant level of concern or fear.
Example: "The report revealed a highly alarming increase in pollution levels in the city."
Alternatives: "extremely concerning" or "deeply troubling".
Harry was incidentally the only journalist ever to travel in Bluebird and for all his bravery as a cragsman, he found the experience highly alarming.
The endemic clonal dissemination and multi-drug resistance of CRPA isolates in our institution is highly alarming.
Orbán's pronouncement highly alarmed the opposition and prompted an outraged reaction in the foreign press.
A spokesman for the United Nations secretary general, Ban Ki-moon, said Mr. Ban was "highly alarmed by the excessive use of force employed by the security forces against protesters" and underlined "the importance of an atmosphere of calm to support Egypt's electoral process as part of its transition to democracy and the early establishment of civilian rule".
I was highly alarmed by the information I was receiving.
She, for example, was highly alarmed by the talks I had had with Ronald Reagan in Reykjavik about a world without nuclear weapons, about an agreement to eliminate medium-range missiles.
The US is highly alarmed at the prospect of any increase in tensions between Pakistan and India, not only because of the broad implications for security in the region (both countries possess nuclear weapons) but also because any deployment of Pakistani troops to its eastern border (with India) would lessen its effectiveness fighting militants in its north-western areas (bordering Afghanistan).
It will even sound a highly annoying alarm.
The original and extremely influential Gathering Storm report of 2005 was notable for spreading a highly controversial alarm about a supposed scientist shortage in the United States and introducing corny meteorological metaphors to the national science-policy discussion.
