Canadian Prime Minister Justin Trudeau says he has intelligence that Iran shot down a Ukrainian jet on Wednesday, killing all 176 people on board, while new footage has emerged showing a midair explosion.

Key points: Canadian PM Justin Trudeau said the intelligence indicates Iran shot down the plane

Canadian PM Justin Trudeau said the intelligence indicates Iran shot down the plane An Iranian report initially said the flight encountered technical problems after take-off

An Iranian report initially said the flight encountered technical problems after take-off The FAA warned US airlines from flying over Iranian airspace after missile strikes

The footage from an unknown source appears to show an explosion close to Ukraine International Airlines flight PS752's last transponder position.

It shows a bright object moving through the sky before a burst of light can be seen.

The plane went down shortly after taking off from Iran's capital Tehran.

Among those killed in the crash were 63 Canadians, as well as 82 Iranians, 11 Ukrainians and 10 Swedes, among others.

Prior to the emergence of the footage, Mr Trudeau said intelligence supported the theory that the plane was shot down.

"We have intelligence from multiple sources, including our allies and our own intelligence. The evidence indicates that the plane was shot down by an Iranian surface-to-air missile," Mr Trudeau said.

"This may well have been unintentional."

Rescue workers recover debris at the plane crash scene. ( AP: Ebrahim Noroozi )

Australian Prime Minister Scott Morrison told the ABC's AM program Australia had received the same intelligence as other countries, and that he had spoken to Mr Trudeau about any support Australia could provide.

"It does not suggest that this was intentional," he said.

"If there's anything we can do to assist then of course we will," he said.

During a press conference, Mr Morrison said it was a "terrible" event that required investigating.

"It's absolutely critical that a full and transparent investigation is undertaken into this terrible event and that would include undertaking all efforts to ensure we get recovery of the black box recorder that can obviously inform that investigation," he said.

An initial report by Iran's civil aviation organisation said the plane had experienced an unspecified technical problem.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 41 seconds 41 s Justin Trudeau has called for a thorough investigation into the Ukraine International Airlines plane crash near Tehran.

Mr Trudeau said his Government would not rest until it got closure, transparency, accountability and justice.

He said Canadian Foreign Minister Francois-Philippe Champagne would speak with his Iranian counterpart Javad Zarif to stress the need for a thorough investigation.

Mr Trudeau's announcement came after United States officials said the Ukraine International Airlines flight was most likely brought down accidentally by Iranian air defences.

However, a Pentagon spokesperson told the ABC they could not confirm the story.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 27 seconds 27 s Debris litters the crash site

Earlier, US President Donald Trump said he had suspicions about the crash but gave no other details.

"Somebody could have made a mistake," Mr Trump told reporters at the White House.

Iran denies 'illogical rumours'

In a statement on Thursday local time, Iranian Government spokesman Ali Rabiei denied the plane had been hit by a missile, according to Iranian state TV.

"All these reports are a psychological warfare against Iran … all those countries whose citizens were aboard the plane can send representatives and we urge Boeing to send its representative to join the process of investigating the black box."

The state-run IRNA news agency quoted a foreign ministry spokesman on Friday as saying Iran "has invited both Ukraine and the Boeing company to participate in the investigations."

The spokesman, Abbas Mousavi, says it will also welcome experts from other countries' whose citizens died in the crash.

The head of Iran's of Civil Aviation Organisation, Ali Abedzadeh, denied "illogical rumours" that the airliner had been hit by a missile, news agency ISNA reported.

"Scientifically, it is impossible that a missile hit the Ukrainian plane, and such rumours are illogical," ISNA quoted Mr Abedzadeh as saying.

The Ukrainian airplane carrying 176 people crashed on shortly after take-off from Tehran's main airport, killing all onboard. ( AP: Mohammad Nasiri )

Mr Abedzadeh told CNN that once the plane took off, it flew for five minutes and "the pilot tried to return to the airport but failed".

"How can a plane be hit by a rocket or missile [and then the pilot] tries to turn back to the airport?"

Maxar's Satellite infrared satellite imagery shows the debris field and burned area of the plane crash site near Khalaj Abad in Iran. ( Supplied: Satellite image ©2020 Maxar Technologies )

The Iranian investigative report cited witnesses on the ground and in a passing aircraft flying at a high altitude as saying the plane was on fire while in the air.

It said the three-year-old airliner, which had its last scheduled maintenance on Monday (local time), encountered a technical problem shortly after take-off and started to head toward a nearby airport before it crashed.

The report said there was no radio communication from the pilot and that the aircraft disappeared from radar at 2,440 metres.

FAA warned airlines to cancel flights

The plane was shot down hours after Tehran launched multiple missile strikes on Iraqi bases housing US troops — an act of "revenge" for the US assassination of powerful Iranian General Qassem Soleimani.

About two-and-a-half hours before the Ukraine International Airlines jet took off, the Federal Aviation Administration issued emergency orders prohibiting American pilots and airlines from flying over Iran, the Persian Gulf or the Gulf of Oman.

Rescue workers recover bodies of victims at the scene where a Ukrainian plane crashed. ( AP: Ebrahim Noroozi )

The notices warned that heightened military activity and political tension in the Middle East posed "an inadvertent risk" to US aircraft "due to the potential for miscalculation or mis-identification".

Several large international carriers — including Lufthansa, Turkish Airlines, Qatar Airways and Aeroflot — continued to fly in and out of Tehran after Iran fired missiles at the military bases in Iraq, though some later cancelled flights.

After the FAA notices, 12 airliners took off or landed without incident early on Wednesday at Tehran's Imam Khomeini International Airport, according to data from Flightradar24. Ukraine International Airlines flight 752 was number 13.

"It was awfully peculiar and awfully risky," said Peter Goelz, a former managing director of the US National Transportation Safety Board.

"That's a theatre of war and these guys were acting like there was nothing going on."

Investigators to search for Russian missile debris

The crash killed Iranian, Canadian, Ukranian, Swedish, German and British nationals. ( AP: Chris Young via The Canadian Press )

Ukraine meanwhile outlined several potential scenarios to explain the crash, including a missile strike and terrorism, as Iranian investigators said the plane was on fire before it fell to the ground.

Ukrainian President Volodymyr Zelenskiy laid flowers at the airport of Boryspil, where the crashed plane was based, and declared January 9 a day of national mourning.

In a television statement, Mr Zelenskiy asked people to refrain from manipulation, speculation, conspiracy theories and hasty evaluations regarding the crash.

Ukraine Security Council Secretary Oleksiy Danylov said the country's investigators wanted to search for possible Russian missile debris after seeing information on the internet.

He referred to an unverified image circulated on Iranian social media purportedly showing the debris of a Russian-made Tor-M1 surface-to-air missile of the kind used by the Iranian military.

Ukrainian investigators into the crash include experts who participated in the investigation into the 2014 shooting down of Malaysian Airlines flight MH17, Mr Danylov said.

'A repeat of MH17'

Chairman of Strategic Aviation Solutions Neil Hansford told the ABC the circumstances described by the Iranians "just had no credibility" and speculated the Ukraine International Airlines flight PS752 was similar to Malaysia Airlines flight MH17 that was shot down on July 17, 2014.

"It didn't deviate, there was no voice recordings, it didn't try to turn back and it complied very well on one engine and it just had no credibility," Mr Hansford said.

"So what's come out is exactly a repeat of MH17."

He also said the pictures of the wreckage indicated it was shot down.

"Something like this, you don't have a field of debris as wide as this for something that's crashed and disintegrated," he said.

"This absolutely disintegrated inflight, as was the case with MH17 when it was taken down by the BUK missile from Russia."

Intelligence and security experts are questioning how the aircraft was shot down by mistake, given the it is one of the most recognisable passenger planes in the world and had only just left Tehran Airport.

John Blaxland is a Professor of International Security and Intelligence at the Australian National University and said world leaders were giving Iran "a lot of doubt" at this point, most likely to avoid a further escalation in tensions.

But he said there were many, serious questions still to be answered.

"I can appreciate why Prime Minister Trudeau and other prime ministers and presidents are wanting to play this down and see this as some sort of accident, but the bottom line is somebody must have given the order to pull the trigger," he told the ABC.

ABC/Wires