The Canterbury Television (CTV) building in downtown Christchurch was engulfed in flames after collapsing in Tuesday's 6.3-magnitude quake, presenting a major challenge in identifying victims, police said.
District commander Dave Cliff said DNA testing could put names to some of the bodies recovered from the building, which housed an English language school, but it was possible some would never be identified.
"Where there is intense fire, like there was at the CTV site, it presents real difficulties," he told reporters.
"I don't want to pre-empt what will happen, but we need to brace ourselves that that possibility does exist. We're not at that point yet, but it presents a risk."
More than 60 students and staff from King's Education remain unaccounted for after the quake, which killed at least 146 people, including citizens from Japan, China, the Philippines, Thailand and Korea.