Boeing could further scale back output on the 737 MAX. (Reuters file photo)

Boeing could further scale back output on the 737 MAX or even "temporarily" halt production if the grounding is extended much beyond current expectations, the company's chief executive said Wednesday.

The aerospace giant has cut output of the planes to 42 a month from 52 since the aircraft was grounded worldwide in March following two deadly crashes.

Boeing's chief Dennis Muilenburg said the plane is expected to resume service in the fourth quarter, but if that drags out the manufacturer "might need to consider possible further rate reductions or other options including a temporary shutdown of the MAX production."