A powerful undersea earthquake south of Japan has shaken buildings in Tokyo and been felt across the country.
The US Geological Survey said the 7.8-magnitude earthquake was centred 874km (543 miles) from the Japanese capital, at a depth of more than 660km.
The earthquake struck at 20:30 local time (11:30 GMT). Buildings in the capital swayed for almost a minute as the quake built in intensity.
There are no reports of serious damage. No tsunami alert was issued.
Commuters are stranded at Ikebukuro station as railway service is disrupted after a strong earthquake hit Tokyo area, Japan, 30 May 2015
Crowds of commuters formed around some of the city's busier stations as trains stopped
However, Tokyo's fire department has received calls about people suffering injuries as a result of falls, broadcaster NHK said.
Reuters reports that services on the Shinkansen high speed train line between Tokyo and Osaka were briefly halted by a power cuts.
Some trains in Tokyo also stopped for safety checks, causing crowds of commuters to form around some of the city's busier stations.
Michiko Orita, a resident of the island of Hahajima, near the epicentre, told NHK: "It shook violently. Our Buddhist altar swayed sideways wildly.
"I have not experienced anything like that, so it was so frightening."
Naoki Hirata, of the University of Tokyo's earthquake research centre, said: "This was a very big quake... the shaking was felt over a broad area... fortunately, because it was deep, there is little danger of a tsunami."
Japan is one of the world's most seismically active nations.
In March 2011, a massive 9.0 magnitude quake started a tsunami that left nearly 20,000 people dead in north-eastern Japan and caused nuclear meltdowns at the Fukushima Dai-Ichi nuclear power plant.
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Drones take whale survey to the sky
In pictures: Drones take whale science to new heights
30 May 2015
From the section Science & Environment
gray whale from above
Gray whales can weigh more than 30,000kg
Instead of standing on the shore with binoculars, scientists are turning to drones to monitor wild populations of whales off the US coast.
A hexacopter hovers 40m or more above the ocean, kitted out with a high-resolution camera to record valuable images of these huge beasts.
Researchers can use these pictures to count the whales, but also to study their health and their behaviour.
This will allow a thorough survey of the gray whales living off California.
"We can't put a gray whale on a scale, but we can use aerial images to analyze their body condition - basically, how fat or skinny they are," said John Durban, a marine mammal biologist at Noaa Fisheries.
Gray whales reach up to 15m in length and can live for more than 50 years. The amount of fat that they carry is crucial - especially for a mother nursing a calf.
two mothers and calves
Blubber is crucial for survival: the skinny mother on the left may not have enough reserves for her to reach the Arctic while nursing her calf
This is because the beasts don't eat during the long months they spend migrating. So they need a healthy stock of blubber if they are to reach their summer feeding grounds in the Arctic.
Studying the animals from the air allows Dr Durban and his colleagues to compare their size, between different animals but also over time.
"By studying the body condition of females, we hope to connect the dots between conditions in the Arctic one year and calf production the next," he explained. "Ultimately, we're trying to understand how environmental conditions affect the reproductive success of the population."
drone landing
The researchers used to watch from the shore with binoculars to count the whales and their calves
These whale were hunted nearly to extinction but after legal protection was introduced in the second half of the 20th Century, they recovered. In 1994, the Pacific population of gray whales officially came off the US endangered species list.
This makes them a valuable subject for research - since most other large whales are still threatened or endangered, there are very few opportunities to see how larger populations interact with each other and their environment.
"With gray whales, we're just beginning to understand what a recovered population of large whales looks like," said Dr Durban.
The team has also used drones to look at killer whales off the coast of British Columbia, in Canada.
family of killer whales from above
Dr Durban's team also used drones to observe killer whales - like this family of seven
The height of the hexacopter is a key concern, because whales and other marine species are sensitive to disturbances in their environment. So the contraption is fitted with a precise altimeter to monitor how high it is. That helps with analysing the pictures, but also means it can keep a safe distance.
The researchers keep their drone at least 40m above the water, and flying at that height requires a special research permit. For amateur drone or wildlife enthusiasts, regulations require a minimum distance of at least 300m.
killer whales nuzzling
Drones offer a new window on the animals' behaviour; here, two killer whales are nuzzling each other playfully
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