"At a very basic minimum those families deserve a thorough investigation that can't take place when essentially rebels aren't giving free access to the corridor of devastation."
The Ministry of Foreign Affairs and Trade had today told Mr Key access was still being restricted.
New Zealand would be represented in Ukraine during the crisis, he said.
"We have sent our consulate from Moscow I think, over to Kiev, so there's someone there already.
"Certainly we're continuing to monitor everything that's going on."
Mr Key said he was concerned that days had gone by, the site was unprotected and only 198 bodies had been removed.
"How can you have a proper and thorough investigation when you've got a crime scene that has got free access to rebels and anybody else?"
President Putin was not showing "real leadership" over the issue, Mr Key said.
"If he was he would be forcing the rebels to essentially have a ceasefire that lasted a lot longer than 24 hours.
"He would be recognising the enormity of what has taken place here and show dignity to those families, and I don't think that's happening."