Air Canada has said that its fleet of Boeing 737 MAX jets will remain grounded until at least August 1, pushing back a previous estimate for their return to service.

Two Boeing 737 MAX aircraft -- one operated by Ethiopian Airlines and another by Lion Air -- have crashed in recent months, killing nearly 350 people.

Air Canada's 24 MAX jetliners were grounded in March following the second crash. At the time, Canada's flagship airline estimated it would get them back in the air by July 1.

It was also expecting to receive 12 more of the planes in July, but Boeing has advised that deliveries of the aircraft have been suspended.

"With the continued grounding of the Boeing 737 MAX aircraft, Air Canada is prudently adjusting its schedule and is finalizing arrangements for additional aircraft to transport customers to their destinations," executive vice president Lucie Guillemette said in a statement.

She said the company has suspended some routes, substituted different aircraft on others, and is finalising deals with other airlines to temporarily operate flights on its behalf from Canada to Europe and to Hawaii.

Boeing executives, meanwhile, said Wednesday they are working closely with the US Federal Aviation Administration and other regulators to return the 737 MAX to service, but gave no timetable.

Analysts have predicted the planes could resume service in late summer or fall.