(CNN) -- Qantas, Australia's national airline, grounded its Airbus A380 fleet indefinitely after part of a plane's engine cover fell off in flight Thursday.
The airline said that flights of the twin-deck planes -- the world's largest airliners -- will remain suspended until an investigation into Thursday's incident is complete.
"As long as it takes," airline CEO Alan Joyce said when asked how long the suspension would last. "We are being very cautious until we know exactly what caused this."
But Singapore Airlines, which suspended flights of its 11 A380 flights shortly after the Qantas incident, has resumed the flights following precautionary checks. Eight aircraft were back in the air late Thursday or early Friday.
"The checks were carried out following advice from engine manufacturer Rolls-Royce and aircraft manufacturer Airbus," a statement on the airline's website said Friday.
One of the four engines on a Qantas airliner shut down six minutes after takeoff Thursday from Singapore's Changi Airport, Joyce said. The plane -- with 440 passengers and 26 crew members -- was headed to Sydney, Australia, but it returned to Changi.
While above the western Indonesian island of Batam, part of the engine's covering, or cowling, tore off.
"I am not sure what actually happened with the debris and why parts of the engine left the aircraft and fell into the ground," Joyce said. "We're still looking at what exactly was the cause of that."
Damage to the wing was was visible in a video shot by a passenger.
The pilot made an announcement updating passengers during the flight.
"I do apologize," the pilot said. "I'm sure you are aware we have a technical issue with our number two engine. We have dealt with the situation. The aircraft is secure at this stage. We're going to have to hold for some time whilst we do lighten our load by dumping some fuel and a number of checklist [items] we have to perform.
"I'm sure you are aware we are not proceeding to Sydney at this stage. We're making a left turn now to track back toward Singapore, and as we progress with this we'll keep you informed, but at this stage everything is secure, the aircraft is flying safely, and we'll get back to you very shortly with further information. Thank you for your patience."
Local television stations in Indonesia showed debris parts with red-white markings. Pictures of the Airbus A380 after it landed showed the cowling torn off in the back half.
Trifuadi, a security officer at an engineering firm in Batam, said he heard a loud explosion and saw smoke coming out of the engine of a plane flying overhead.
Shortly afterward, debris fell from the plane to the ground, said Trifuadi who, like many Indonesians, goes by one name.
The flight -- QF32 -- landed in Singapore safely, without injury to passenger or crew.
Passenger Meg Graham said she heard a loud bang within minutes of the plane taking off. "And then another bang," she said.
Ulf Waschbusch, who said he was on his way to Australia for the first time, said the crew kept passengers apprised of what was happening.
"We all stayed pretty calm," he said. "It was an almost eerie calm."
"It feels a lit bit like watching a Hollywood movie rather than actually being inside of it," said Waschbusch, who had a window seat.
People didn't talk much, and the plane circled for more than an hour, the passenger said.
"The fact that you can have an engine blow up, through the wings, and this thing still flies safely and lands safely is fascinating," he said.
The airline said it will work with the plane's manufacturer as well as Rolls-Royce, the maker of the engine, to determine what went wrong. A spokesman for Rolls-Royce said "safety is always our highest priority. We are currently analyzing the available information and working with our customers to support their operations."
Qantas has six A380s in its fleet of 191 planes. Airbus will at some point deliver another 14, the airline said.
Lufthansa, which operates three Airbus A380s, said it is planning to carry out additional precautionary checks on the engines of the planes. The airline is waiting for more detail from Rolls-Royce about the specific checks that need to be carried out before proceeding.
China's state-run aviation supplier signed for 102 Airbus aircraft Thursday, 66 of them new orders. The country is buying 50 A320s, six A330s and 10 A350 model aircraft.
CNN's Christabelle Fombu, Nicky Robertson, Judy Kwon, Kevin Voigt, Liz Neisloss, Ayesha Durgahee and Mia Anngre contributed to this report.