Officials said the investigation would take days, if not weeks.
The group of investigators is accompanied by monitors from the Organization for Security and Co-operation in Europe, also known as OSCE.
Foreign experts at the site are seeking human remains from the crash; the Australian foreign minister said Thursday that there could be as many as 80 unrecovered bodies.
Efforts to reach the crash site had been previously stymied by heavy fighting between pro-Russian separatists and the Ukrainian military.
Morgan reported that investigators were able to access the site after both the separatists and the Ukrainian military agreed to provide a safe corridor for entry.
Fighting surrounding the crash site, however, has remained intense, and the region is “very volatile,” according to Morgan.
A week after Malaysia Airlines Flight 17 was shot down over war-torn eastern Ukraine, dozens more coffins containing remains of victims of the crash were due to arrive in the Netherlands on Thursday.
They will follow the first 40 wooden caskets, which were flown in Wednesday and greeted by somber, moving tributes across the country.
A lone bugler sounding the traditional military farewell "Last Post" marked their arrival at a military base in Eindhoven.
The grieving nation then held a moment of silence to honor those killed in the crash of the jetliner - caught in a war in which they had no part.
The plane was downed last week by a suspected surface-to-air missile over eastern Ukraine, where groups of pro-Russian rebels are battling Ukrainian government forces.
In a reminder of the ongoing bitter conflict, rebels claimed responsibility for shooting down two Ukrainian military jets on Wednesday. The rebels have denied that they brought down Flight 17.
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After spending days exposed to the elements on a Ukrainian field and then inside refrigerated train cars, the first group of victims from Malaysia Airlines Flight 17 are one step closer to home.
The first plane carrying the remains of some victims are expected to arrive in the Dutch city of Eindhoven on Wednesday.
The arrival will mark a homecoming for many of the victims. Most of the 298 people on board the plane were from the Netherlands, which has declared Wednesday a national day of mourning.
Dutch royals, government officials and families of the passengers will be at the tarmac when the remains arrive. After a solemn ceremony, the bodies will be taken to a military facility for forensic testing.
But Dutch Prime Minister Mark Rutte said it could take weeks or even months to identify the remains.
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A train carrying 282 bodies from Malaysia Airlines Flight 17 arrived in Kharkiv, Ukraine, getting the bodies one step closer to their grieving families around the world.
The train arrived at a rail station and continued on to an undisclosed location. The bodies will eventually be taken to the Netherlands.
But a litany of obstacles remain - not just in handling the remains, but in figuring out how and why MH17 was shot down over eastern Ukraine.
See more on this developing story on CNN.com.
There's no shortage of evidence that shows pro-Russian rebels shot down a Malaysian jet in Ukraine last week, U.S. Secretary of State John Kerry said.
Malaysia Airlines Flight 17 fell from the sky in Donetsk on Thursday, killing all 298 people aboard.
There's video of a launcher with one surface-to-air missile missing, imagery showing the firing and intercepted calls with rebels claiming credit for the strike, Kerry said.
"We know from intercepts ... that those are in fact the voices of separatists," he told CNN's State of the Union on Sunday. "And now we have a video showing a launcher moving back through a particular area there out into Russia with at least one missing missile on it."
Kerry accused Russia of backing the separatists.
"This is the moment of truth for Russia. Russia is supporting these separatists. Russia is arming these separatists. Russia is training these separatists. And Russia has not yet done the things necessary in order to try to bring them under control," he said.
British Prime Minister David Cameron didn't mince words either on who was to blame. In an op-ed in The Sunday Times, he called the plane crash and its aftermath "an outrage made in Moscow."
Russian President Vladimir Putin fired back with a video statement posted on the Kremlin's official website early Monday, arguing that his country has been pushing for peace in Ukraine.
"We have repeatedly called on all parties to immediately stop the bloodshed and to sit down at the negotiating table. We can confidently say that if June 28 fighting in eastern Ukraine did not resume, this tragedy most likely would not have happened," he said. "However, no one should have the right to use this tragedy to achieve selfish political objectives. Such events should not divide but unite people."
He stressed that safety must be guaranteed for international experts investigating the crash.
"We must do everything to ensure their work has full and absolute security (and) ensure necessary humanitarian corridors are provided," Putin said.
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A Malaysia Airlines passenger jet crashed in a rebel-controlled part of eastern Ukraine on Thursday, spurring swift accusations from Ukrainian officials that "terrorists" shot down the aircraft.
The United States has concluded a missile shot down the plane, but hasn't pinpointed who was responsible, a senior U.S. official told CNN's Barbara Starr.
The Boeing 777 with 298 people aboard fell from the sky near the town of Torez in the Donetsk region of eastern Ukraine, officials said. A top Ukrainian official said the plane, which was on the way from Amsterdam to Kuala Lumpur, was flying at about 10,000 meters (nearly 33,000 feet) when the missile hit.
A radar system saw a surface-to-air missile system turn on and track an aircraft right before the plane went down, the senior U.S. official said. A second system saw a heat signature at the time the airliner was hit, the official said. The United States is analyzing the trajectory of the missile to try to learn where the attack came from, the official said.
The Obama administration believes Ukraine did not have the capability in the region - let alone the motivation - to shoot down the plane, a U.S. official told CNN's Jake Tapper.
Malaysian Prime Minister Najib Razak said the plane never made a distress call.
He called for an international team to have full access to the crash site.
"We must and we will find out precisely what happened to this flight. No stone will be left unturned," he said.
"If it transpires that the plane was indeed shot down, we insist that the perpetrators must swiftly be brought to justice," Najib said.
Ukrainian officials maintained that pro-Russian separatists were behind the crash.
You can follow the updating story at CNN.com