TOKYO (AFP) - Japan's top court has upheld a ruling awarding millions of dollars in compensation to families of children swept out to sea in the massive 2011 tsunami, officials said on Friday (Oct 11).

In all, 74 children from Okawa Elementary School in the city of Ishinomaki drowned after being told to wait on school grounds with teachers, 10 of whom also died, instead of seeking higher ground.

The 29 plaintiffs - parents of 23 children who died in the disaster - argued their children would have survived if they had been evacuated in time.

The Sendai district court ruled in 2016 that two local governments should pay a combined 1.43 billion yen (S$18 million) to the plaintiffs.

That ruling was upheld in 2018 by the Sendai High Court, and on Thursday, Japan's Supreme Court rejected an appeal by the local governments, a court spokesman said.

"This is historic," the plaintiffs' lawyer Kazuhiro Yoshioka told AFP.

"This means that the Supreme Court agrees with the high court that schools across the country... have to do their best in ensuring children's safety," he added.

The high court ruled that the teachers should have been able to forecast before the occurrence of the quake that a tsunami would reach the school.

A huge undersea quake in March 2011 sent the tsunami barrelling into Japan's north-eastern coast, leaving about 18,500 people dead or missing, and sending three reactors into meltdown at the Fukushima nuclear plant.

Contacted by AFP, an Ishinomaki official said the city "has been making steady progress in safety measures against potential disasters since the 2011 tsunami", but could not immediately comment on the ruling.

Miyagi prefecture officials also could not immediately comment on the verdict.