The remains of children have been found in the rubble of a collapsed apartment building near Miami for the first time.

Miami-Dade mayor Daniella Levine Cava announced the death toll stood at 18, saying the remains of sisters Emma, four, and Lucia Guara, 10, had been identified and called the loss "too great to bear".

Ms Cava spoke haltingly and said the disclosure came with "great sorrow, real pain".

"So any loss of life, especially given the unexpected, unprecedented nature of this event, is a tragedy," she added.

The sisters' parents' remains have also been recovered, authorities said.

Officials also confirmed they had found four additional victims - the total of six on Wednesday was the highest one-day death toll so far.

Ms Cava said the number of residents unaccounted stands at 145.

No-one has been found alive since hours after the collapse on June 24.