The death toll after the collapse of a Florida apartment tower has risen to nine, officials said on Sunday after rescue teams recovered four more bodies from the rubble.

A large section of the 12-story oceanfront Champlain Towers South in Surfside collapsed in the middle of the night on Thursday as residents slept.

Miami-Dade Country officials say more than 150 people are still missing.

So far, four of the nine have been identified by police. "We are making every effort to identify those others who have been recovered," Miami-Dade County Mayor Daniella Levine Cava told reporters.

One of the victims had died in the hospital, Cava added.

Search for the missing continues

Rescue teams carefully picked through the rubble for a fourth day without finding further signs of life.

Two large cranes and two backhoes on Sunday joined in the debris-removal efforts.

Previously, the search had been conducted largely by hand by teams also using rescue dogs, sonar, drones and infrared scanners.

Rescuers were also using a microwave radar device developed by NASA's Jet Propulsion Lab and the Department of Homeland Security that "sees" through solid concrete, according to Adrian Garulay, CEO of Spec Ops Group.

Israeli and Mexican engineers and search-and-rescue specialists joined the search teams at the site.

"This is one of the best and the most experienced Israeli rescue teams," Israeli diaspora affairs minister Nachman Shai said as the team arrived early Sunday.

Crews spent Saturday night digging a large trench that allowed them to find more bodies and human remains.

A smoldering fire beneath the rubble that hindered the work of rescuers had abated by Sunday morning, officials said.

Relatives visit site

Buses brought several groups of relatives to a place where they could view the pile and the rescuers at work on Sunday.

Families of the missing have expressed mounting frustration and anger at the pace of the rescue operation.

Officials who spoke Sunday repeatedly sought to reassure them that everything possible is being done: "We're moving as fast as we can, as hard as we can," Miami-Dade fire chief Alan Cominsky told reporters.

Cava also visited the site praised the rescue workers as the "the best in the world."

Residents in 'sister' tower can evacuate

Surfside Mayor Charles Burkett said accommodation was being found for anyone wishing to evacuate the tower's nearly identical "sister" building a block away, although no structural problems have yet been identified there.

On Friday, an engineer's survey conducted in 2018 into the condition of the now-collapsed building emerged. It pointed to "major structural damage" in the building.

kmm/wmr (Reuters, AP, AFP)