UPDATED 3.35PM | The Bangladeshi passenger on a Dubai-bound flight who threatened to blow up the plane and tried to force his way into the cockpit was carrying a toy gun and no explosives, police said on Monday.

Police are investigating how the man had been able to board the Biman Bangladesh Airlines flight in Dhaka on Sunday in the first place.

The Boeing 737-800 made an emergency landing in the southern port of Chittagong where commandos stormed the plane and shot the would-be hijacker, officials said. All 148 passengers and crew safely disembarked, police said.

The hijacker died later of his injuries.

"The pistol with the suspect was a toy pistol and he had no bomb attached to his body,” said Kusum Dewan, additional commissioner of Chittagong police.

“He appeared to be mentally imbalanced. We heard he had a personal issue with his wife and demanded to speak to the Prime Minister Sheikh Hasina. But we are still investigating. We don’t want to come to any conclusions right now."

Air Vice Marshal Nayeem Hasan, chairman of the Civil Aviation Authority, said it was a mystery how the man, believed to be in his 20s, had managed to board the plane.

“It was the responsibility of the Civil Aviation Authority to search each passenger before boarding and it was done for this aircraft also, but it is a big question to us that how he boarded with a pistol," he told Reuters.

"Now we are focusing on two issues – his background and identity and the security aspect that how he boarded with a pistol."

“We tried to arrest him or get him to surrender, but he refused and then we shot him,” said Major General S M Motiur Rahman of the Bangladesh Army.

The man’s threat to blow up the plane, which was on its way to Dubai from Dhaka via Chittagong, led its pilots to make an emergency landing.

One crew member had been held hostage, the officials said.

Air Vice Marshal Nayeem Hasan, chairman of the Civil Aviation Authority of Bangladesh, told reporters at a news conference that as well as holding what appeared to be a pistol, the passenger said he had explosives bound to his body.

With the plane close to Chittagong after leaving Dhaka, the passenger stood up from his seat and tried to go to the cockpit, according to aviation officials. When a member of the crew blocked his way, he showed his pistol.

He then said he had explosives and if they didn’t open the door of the cockpit he would blow up the plane, officials said. Other members of the crew alerted the pilots to the problem and they asked air traffic control for an emergency landing.

It was not immediately clear if he had explosives, though the pistol was real, according to a senior aviation official. It also wasn’t immediately clear if the pistol was loaded or how it got through security at the airport in Dhaka.

The security questions are a matter of concern and would be the subject of an investigation, said the aviation official.

The man appeared to be in his 20s, and was probably Bangladeshi as he was speaking Bangla, but his identity was not yet clear, Hasan said.

- Reuters.