(Updates with figures, comments)
By Chisa Fujioka
HACHINOHE, Japan, July 24 (Reuters) - A strong earthquake jolted northern Japan early on Thursday, injuring more than 100 people, trapping hundreds in halted trains and affecting production at some high-tech factories.
The quake, which struck at 00:26 (1526 GMT Wednesday) and had a preliminary magnitude of 6.8, the Japan Meteorological Agency said, was the latest in a series to hit the sparsely populated, mountainous regions of Iwate and Aomori.
A National Police Agency official said 107 people were injured, 16 seriously. Many were hurt in falls or suffered cuts from broken glass.
Officials warned of possible landslides, and hundreds of homes were without running water, broadcaster NHK said.
At Choryuji temple in Hachinohe, about 550 km (340 miles) northeast of Tokyo, one of the worst hit towns, rows of tall gravestones were knocked over and some were broken.
"It’s such a shock to see this mess," said 77-year-old Toshikatsu Sawashiro, who came to check his family grave.
A local government building in the same area was also a mass of broken glass, with fallen ceilings and toppled shelves.
Earthquakes are common in Japan, one of the world’s most seismically active areas. The country accounts for about 20 percent of the world’s earthquakes of magnitude 6 or greater.
Thursday’s tremor follows a string of earthquakes in the same region, the first of which in mid-June killed at least 10 people and left as many again missing.
The damage was relatively minor in Thursday’s quake because its focus was more than 100 km (62 miles) underground, a seismologist said.
"It was deep," said Naoshi Hirata, a professor of geophysics, at Tokyo University. "A shallow quake of magnitude 6.8 would cause a lot of damage, but a quake deep underground is the same as one that’s far away."
Hundreds of people were initially trapped on overnight trains that were halted after the quake, but were later able to get out safely, rail operator JR East said. Service was set to resume on high-speed bullet trains, but many local trains were still not running 12 hours after the tremor.
Some stretches of expressway were briefly closed to traffic in the region, but they were later reopened, said a spokesman for the operators. Some smaller roads remained blocked by landslides.
With few strong aftershocks to hamper operations, the clean-up started almost immediately. Most schools in the region were open as usual and phone and electricity services were restored, providers said.
"There were no reports of deaths or people buried alive," top government spokesman Nobutaka Machimura told reporters. "But the prime minister has ordered us to continue checking."
Tohoku Electric (9506.T) and Tokyo Electric (9501.T) said their nuclear power plants in northern Japan had not been affected.
Fujitsu Ltd (6702.T) said it stopped production lines at a semiconductor factory in Iwate, and Toshiba Corp (6502.T) and NEC Corp (6701.T) said they had stopped chip plants for checks.
But Tohoku Electric said it restarted a 250-megawatt oil-fired power plant in Aomori that was shut down after the quake. Nippon Steel (5401.T) also restarted steel output at its Kamaishi works.
In October 2004, an earthquake with a magnitude of 6.8 struck the Niigata region in northern Japan, killing 65 people and injuring more than 3,000.
That was the deadliest quake since a magnitude 7.3 tremor hit the city of Kobe in 1995, killing more than 6,400. (Additional reporting by Yoko Kubota, Chris Gallagher, Isabel Reynolds, Osamu Tsukimori, Linda Sieg and Yoko Nishikawa; Editing by Hugh Lawson)