Massachusetts ? Investigators got their first close-up look Friday at a chemical plant leveled by an explosion, saying the damage was so extensive that they don’t know the precise point of the blast.

A team of local, state and federal officials briefly examined the charred wreckage Friday afternoon after a hazardous materials team checked the site to ensure it was safe for investigators, who wore respirators as a precaution.

The lengthy probe into the cause of Wednesday’s blast was expected to continue through the weekend.

About 10 homes were destroyed and another 60 were damaged when the blast obliterated the former CAI Inc. chemical plant. No serious injuries were reported.