Aftershocks as strong as magnitude 6.0 rocked Turkey into the night, following a 7.2-magnitude earthquake hit that eastern Turkey earlier today, leveling dozens of buildings and leaving at least 138 people dead.
There were at least four aftershocks of magnitude 5.1 or greater throughout the day, as aide workers and rescuers worked to help the victims.
At least 59 people have been killed and 150 hurt in Ercis, according to a state-run television station.
Ercis mayor Zulfikar Arapoglu told NTV television that the region need urgent medical aid.
"There are so many dead," he said.
About 15 people died in the city of Van, with the death toll there expected to rise.
An estimated 1,000 people could have been killed, based on the size of the quake and weak housing codes, The Associated Press reported.
The quake, which struck the region at 1:41 p.m. local time, was upgraded from a preliminary magnitude of 6.6 to 7.3 magnitude. The U.S. Geological Survey later revised the magnitude to 7.2.
The depth of the epicenter was considered shallow -- 12.4 miles, shallower than the earthquake that devastated Haiti in January 2010 -- and more potentially destructive, combined with the poor building codes in the region.
The temblor's epicenter was in the village of Tabanli, near the city of Van close to the Iranian border, the AP reported.
Van mayor Bekir Kaya told NTV television that the "telephone system is jammed due to panic and we can't assess the entire damage immediately."
State-run media reported rescue crews were working to free people who were trapped under a seven-story building that collapsed.
Residents of Van and neighboring towns poured into the streets as several strong aftershocks rocked the area.
"There are many people under the rubble," district mayor Celebibag Veysel Keser told NTV, the AP. "People are in agony, we can hear their screams for help. We need urgent help."
Frederike Geerdink, a journalist in Istanbul, said she didn't feel it, but there are reports of a lot of damage where the quake struck.
"There's a lot of damage," she said. "Like people are in general not well prepared for earthquakes in Turkey."
Earthquakes and seismic activity are nothing new to Turkey, as the area is riddled with faults, but the USGS said today's quake is the biggest to hit in the region in more than four decades.
The last major earthquake to hit the country was in 1999, when 18,000 people were killed, according the AP.
President Obama said he has been following the reports on the quake today.
"Our thoughts and prayers are with the brave men and women who are working to bring assistance to this stricken region. We stand shoulder to shoulder with our Turkish ally in this difficult time, and are ready to assist the Turkish authorities," Obama said in a statement.
ABC News Radio and The Associated Press contributed to this report.