Are you there? Please send us your photos, videos and stories.
[Updated at 4:00 p.m. ET] The U.S. Geological Survey has again revised the magnitude of the Mexican quake, down to 7.4.
[Updated at 3:29 p.m. ET] Though the epicenter was about 175 miles from Mexico City, earthquakes are a frightening experience for the city's more than 20 million residents of Mexico City. About 10,000 people perished in a massive quake in 1985.
The city, built on volcanic ash and clay, is particularly vulnerable to temblors.
Read CNNMexico's coverage in Spanish
[Updated at 3:17 p.m. ET] Local authorities in Guerrero state have reported aftershocks, while residents in Oaxaca and Guerrero states and the eastern state of Veracruz reported that phone service had been knocked out in their areas.
[Updated at 3:12 p.m. ET] Pascal Clemens, a businessman in Acapulco, says he has lived in the city for 17 years, and Tuesday's earthquake was in the top five of those he's experienced in that time.
It was "a pretty strong one," he said.
[Updated at 3:03 p.m. ET] A real estate agent in Acapulco told CNN International that he was in an office building when the quake hit. He said that the area has felt tremors for a while now, “but not strong like this one.”
Footage in Mexico City showed people milling around outside office buildings moments after evacuating.
[Updated at 2:42 p.m. ET] Tourists and residents told CNN they felt the earthquake in the resort city of Acapulco, which, according to the U.S. Geological Survey, is about 120 miles west of the epicenter.
Mexican President Felipe Calderon said in a Twitter post that there were no immediate reports of serious damage.
Lea este artículo en español/Read this article in Spanish
In Mexico City, Mayor Marcelo Ebrard sent tweets saying there was no visible damage in the capital and that the sprawling city's strategic services and water system were functioning.
Regardless, he tweeted, numerous buildings were being evacuated.
[Updated at 2:33 p.m. ET] Eleven miles is about the same depth as the devastating Haitian quake of 2010, according to CNN meteorologist Chad Myers, who said the region can expect aftershocks.
The epicenter was about 15 miles east of Ometepec in the Guerrero region, according to the U.S. Geological Survey.
There were no immediate reports of damage or injuries.
[Updated at 2:28 p.m. ET] Updated information from the U.S. Geological Survey indicates it was a 7.6-magnitude earthquake. It struck at a depth of almost 11 miles.
[Updated at 2:24 p.m. ET] CNN's Nick Parker in Mexico City said the earthquake lasted about 10 or 15 seconds.
"The room I was in rattled. A few vases rattled around," he said.
[Updated at 2:21 p.m. ET] The U.S. Geological Survey is reporting that the temblor that struck the Mexican capital registered a preliminary magnitude of 7.9.
It struck in the Guerrero region, with its epicenter about 92 miles west of Oaxaca and about 120 miles east of Acapulco.
[Posted at 2:16 p.m. ET] Residents rushed into the streets of Mexico City on Tuesday after a strong earthquake hit.
It's actually nowhere near the capital. But it is near some heavily populated areas. Google "USGS earthquake map" for detailed info. And it's been downgraded to 7.6. This will probably be bad.
Only 11 miles deep.
It's the spirit of Mexico trying to shake Obama's daughter and her friends out of the country. Wish it would happen in Washington.
track the quake and see where it pops up next-either as an other quake or volcanic burp of some sort
We felt a earthquake here at PNG.
Andrew, where's PNG?
Papua New Guinea?
There was a 6.2 quake a few minutes earlier in Papua New Guinea. Andrew is referring to that. The USGS website has lots of cool data, for nerds like me.
not me @ 2:49
The President said the water systems are functioning...good one.
I live about 8 miles outside of Acapulco and did not feel a thing!
Almost the same as the Haitian Earth Quake , proof that it has nothing to do on how you build a house , it depends on oh it hits and whether it s Shallow or not , Mexico has a lot of Antiquity homes there m they are lucky that it didn't hit in a populated area or Historical places with old buildings and priceless ruins . WOW , when will these Earth Quakes stop.
Where Next ?
OH GOD IT'S EARTHQUAKES OH GAWD!!!!!!!!!!!!!!!!!!
CNN MUST REPORT ON EVERY EARTHQUAKE IN THE WORLD OR ELSE THE WORLD WILL END!!!!!!!!!!!!!!!!!!!!!
Did ever think there just that many earthquakes happening? 7.9 is not a small one and if you live on the West Coast you know should never take one of that magnitude lightly.
7.6 is pretty substantial. Don't be an idiot.
DONT WORRY MAN!!!!! lots more coming...soon the word quake will have u trembling and crying for ur mommy...u willl learn the hard way...wake up wake up wake up!!!!
PNG–Papua New Guinea.
PNG- Papua New Guinea
WOW, called someone a few minutes ago in Mexico CIty to help them with some PC trouble and he said the shaking had just stopped in the building and they were evacuating now!!! crazyness!!!
That's a pretty big earthquake. I hope everyone is safe.
Here in Mexico City everything is fine! back to normal, at least it seams like that. Mobile lines are saturated, and regular lines too, they were down for a few minutes.
The Mayan's were Right!
u know that charged particles hit earth 2 days ago...they came from somewhere past the sun!!!!!thers alot more to come man stay safe!
This blog – This Just In – will no longer be updated. Looking for the freshest news from CNN? Go to our ever-popular CNN.com homepage on your desktop or your mobile device, and join the party at @cnnbrk, the world's most-followed account for news.