An earthquake with a magnitude of 6.1 struck off northeastern Japan on Wednesday, the US Geological Survey (USGS) said. There was no immediate tsunami warning, or reports of damage or casualties.
Shortly afterwards, a magnitude 6.2 earthquake shook Ecuador's coast, terrifying locals and impeding rescuers after a more severe weekend quake battered the same area and killed hundreds of people.
According to an official, the death toll in Ecuador from initial earthquake has risen to 525, Agence France Presse reported.
A series of strong quakes struck the south of Japan late last week, killing nearly 50 people. On Wednesday, survivors struggled with shortages of food and water.
The USGS said Wednesday's quake was centred 104 km east southeast of Sendai, Honshu, near an area where a devastating quake and tsunami struck in March 2011. It was 51 km deep.
The latest earthquake in Ecuador hit 25 km off Muisne on the northwest Pacific coast at a depth of 15 km, it also said.
That was near the epicentre of Saturday's 7.8 quake, which devastated a long swath of the coast and dealt a major blow to the oil-producing nation's already fragile economy.
Witnesses said two strong tremors of about 30 seconds each woke people up and sent them running into the street.
No tsunami warning was issued, and there were no immediate reports of major damage.
Ecuador's Geophysical Institute said there were in fact two quakes of magnitude 6.2, followed by 17 aftershocks. The USGS, however, mentioned one quake of size 6.1.
Local media reported that rescue operations were temporarily suspended because of the new earthquake, amid dwindling hopes of finding more survivors from Saturday's quake.
That earthquake killed 480 people, left another 107 missing, and injured more than 4,600. It also destroyed about 1,500 buildings, triggered mudslides and tore up roads.
Some 20,500 people were left sleeping in shelters.