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.