Top US Senate Republican Mitch McConnell appeared briefly unable to speak at a news conference on Wednesday, marking the second time in recent weeks that the 81-year-old has abruptly frozen at a public event.

McConnell was answering reporters' questions in his home state Kentucky when he fell silent for around 30 seconds, despite being prompted by an aide.

"Did you hear the question, senator?" the staffer asked after an awkward pause and, as McConnell continued to be unresponsive, she told the room: "I'm sorry, you all. We're going to need a minute."

"Leader McConnell felt momentarily lightheaded and paused during his press conference today," his spokesman said later.

President Joe Biden told reporters at the White House he was going to get in touch with McConnell.

"(We) have had disagreements politically, but he's a good friend," he said.

It is the senator's second health scare since July, when he froze mid-sentence during a press conference in Congress and stood motionless at a microphone for about 20 seconds before aides and fellow senators led him away.

At that time, the veteran politician returned several minutes later and told reporters he was "fine" before taking questions.

McConnell has been the top Republican in the US Senate since 2007, and wielded unflinching power as majority leader from 2015 to 2021.

He notably engineered conservatives taking a majority on the Supreme Court by stalling a confirmation hearing for Barack Obama's nominee in 2016 and ensured that Trump was not convicted after his unprecedented two impeachments.

In March, McConnell was hospitalized after he tripped and fell during a private dinner. He suffered a concussion and a fractured rib, and spent six weeks away from the Senate, undergoing physical therapy.

An aide said McConnell would consult with a physician before his next event.