BEIJING - An earthquake struck Wenchuan in the eastern part of Sichuan province this afternoon, hitting 7.8 on the Richter scale. This report indicates it registered as a 3.9 quake as far away as Beijing.

The Guardian picks it up from here:

The quake hit 57 miles (92km) north-west of Sichhuan, the capital of Chengdu province, at 2.28pm (7.28am BST), the US Geological Survey said on its website.
It was not immediately clear if there were any casualties or damage in the provincial capital.
"We felt continuous shaking for about two or three minutes. All the people in our office are rushing downstairs. We're still feeling slight tremblings," said an office worker in Chengdu.
Tremors were felt in Beijing, about 930 miles away, and the Thai capital of Bangkok, 2050 miles away, where buildings swayed for several minutes, although there were no immediate reports of injuries.
In Beijing's financial district, many workers left their buildings but there were no visible signs of damage.

Your's truly was sitting at Starbucks on the 2nd floor of Tower 2 of the China World Center when the quake struck, and was completely oblivious that anything had occured. It wasn't until I received a phone call and was told an earthquake had just struck was I made aware. I immediately glanced up at the looming CCTV tower and saw that it was still standing, so I figured it couldn't have been that bad.

The office buildings in Guomao were evacuated, leaving thousands of people on the streets.

UPDATE 1 (12:47am Beijing Time):

This quake looks to be much stronger than first anticipated. My phone has been ringing off the hook all night from news organizations in Canada wanting live interviews and more information. Unfortunately I'm in Beijing and not in Sichuan, so I'm only able to provide information from Xinhua and Twitter, as well as the excellent coverage from Global Voices and Shanghaiist (which deserves a mention "with honors" for its updates all day).

The death toll seems to be increasing almost hourly. Since I began doing live hits, it has risen from 5,000 to 7,600 and now I'm reading it could be over 8,000. As soon as I post this, I'm sure it will be outdated.

I also notice that, as far as I can tell, only the New York Times is reporting that the tremors felt in Beijing likely weren't the same ones from the earthquake in Sichuan. It claims a second quake hit Tongzhou shortly before 3pm which caused the swaying buildings and chandeliers in the capital. I'm sure more on this will come to light in the coming hours and days.

Our hearts go out to all the victims and their families and friends in Sichuan and around China.

Update 2 by Paul
(11:05am, Tuesday)

The death toll from yesterday's earthquake in Sichuan has now been upgraded to 9,219. Of course, this is a preliminary estimate. Indications are that rescue crews are still clamoring to try to get to the hardest-hit region of Sichuan, which is Wenchuan (汶川) county, north of Chengdu. Apparently many of the roads have been washed out by landslides. And just taking a look at the forecast over the next couple of days, it doesn't look like rescue crews are going to have any easier a time. The forecast, though warmer than today (26 degrees Wednesday and 30 Thursday), is still calling for showers in the area.

Like Cam, I too have been contacted by a few news organizations, including my old station back in Vancouver which called me at 6:45 this morning (though, it was fine, because I happened to basically be up anyway). I expect this is likely going to continue as more and more information continues to come out about the severity of the quake. On a related topic, I have to give props to the state-run television stations for their coverage. Between devastating footage and reporters giving live updates on a continual basis on CCTV's news channel, I must say it's a lot better than I thought it was going to be. I suspect the government has specifically asked for as much coverage as possible on this, given the fallout from the snowstorms earlier this year. I suspect there is significant concern within government circles right now about civil unrest and rumors, as can be gleaned from this line from a Xinhua report:

"Those who spread rumors to sabotage disaster relief work would be dealt with according to China's laws and regulations."

Almost immediately following yesterday's quake, an SMS rumor started making the rounds (around 3:30pm) in the capital that there was going to be another quake between 10pm and 12am that was going to be larger than the first one felt in Beijing. Obviously, anyone who knows anything about earthquakes knows that science has yet to be able to predict exactly when earthquakes will strike. All that can be done is measure them when it happens. But its rumors like these that the government understandably wants to quash.