The search for victims of Japan’s mega earthquake has gradually expanded across wider areas, with access improved by the removal of debris left by tsunamis, rescue officials said Thursday, the seventh day since the quake.

Meanwhile, fuel shortages have hampered the delivery of relief supplies to shelters where survivors are staying, while also limiting the use of heavy machinery and heating appliances, they said.

The number of those who died or were unaccounted for came to 12,920—4,314 deaths and 8,606 missing, while some 380,000 are still staying in shelters, the National Police Agency said, based on its 8 a.m. tally.

In the severely hit coastal city of Rikuzentakata, Iwate Prefecture, the development in rubble removal has enabled the Self-Defense Forces to build roads so rescue workers can search for victims across wider areas.

Mayor Futoshi Toba said, ‘‘There were some areas where we could not enter, but now we can go anywhere (in the city) by car.’‘

He added, however, ‘‘We need fuels to heat, activate heavy machines and deliver relief goods to shelters, but we face difficulties.’‘

The prefectural government of Miyagi has almost completed confirming isolated areas from the air, and it will start distributing relief materials to these areas by helicopter, its official said.

In Ishinomaki, Miyagi Prefecture, Mayor Hiroshi Kameyama told the municipal task force meeting that the number of missing people in the city of 160,000 will reach around 10,000.

On Thursday, temperatures of the quake-hit areas in northeastern Japan dropped to midwinter level, marking 5.9 degrees below zero in Morioka, Iwate, 2.7 degrees below zero in Sendai, Miyagi, and 3.5 degrees below zero in the city of Fukushima.

As temperatures are expected to remain low in these areas through Friday morning, the Japan Meteorological Agency called on residents to take care.

In another heavily damaged coastal city of Ofunato, Iwate Prefecture, meanwhile, elementary as well as junior and senior high schools reopened for the first time since the outbreak of the quake.

At prefecture-run Ofunato High School, around 250 students arrived on foot or by bicycle. First-grader Ayumi Urashima, 16, said, ‘‘On the way to school, I met one of my friends who I had not been able to contact. We hugged each other.’‘

The Fire and Disaster Management Agency said the number of partially or completely destroyed buildings reached 100,396 as of 7 a.m.