REX denies fire before emergency landing

A Regional Express flight's emergency landing at Merimbula Airport in southern NSW was prompted by a right engine mechanical failure rather than an engine fire, the civil aviation regulator has been told.

The Rex flight on Thursday evening from Sydney to Merimbula via Moruya touched down after experiencing a "cockpit sensor alert", and was greeted by fire and rescue authorities.

The alert obliged crew to shut down the right engine of the Saab 340.

Rex has since informed the Civil Aviation Safety Authority its engineers have found no evidence of an engine fire and that passengers may have misinterpreted engine sparks for a blaze.

"The information we've been given from REX is that there was not an engine fire, there was a mechanical failure which triggered an engine fire warning," CASA spokesman Peter Gibson said on Friday.

"There was excess heat created inside the engine so there was a red glow.

"We'll continue to get reports from REX engineers as they strip the engine down. They haven't pinpointed the cause of the engine failure yet."

There were 19 passengers and three crew on board the flight.

REX said in a statement on Friday they immediately briefed CASA and the Australian Transport Safety Bureau on the incident.