Early this morning, at approximately 6.00 am local time, many people in southern Haiti were alarmed by a strong aftershock  (measured at 6.1 magnitude ), with an epicentre near the town of Petit-Goâve , west of Port-au-Prince. This was the strongest in a series of aftershocks since the major earthquake on 12 January  which devastated the capital and surrounding areas. (Many Haitians whose houses are standing but damaged continue to sleep outdoors as a precaution.)
Online reactions came almost immediately, starting on Twitter. “ Strong aftershock! Danm!”  wrote @carelpedre  (radio journalist Carel Pedre) in Port-au-Prince. “ Major aftershock just now…felt like a five,”  wrote @troylivesay  (charity aid worker Troy Livesay), almost simultaneously.“ Guess we don't need an alarm when the earth shakes and wakes you up as if you were late for an urgent meeting,”  commented @olidups  (Olivier Dupoux). It was also reported by @bibinetallez  (Fabiola Coupet) in Petionville and @yatalley  (blogger Yael Talleyrand ) in Jacmel.
@RAMhaiti  (musician and hotelier Richard Morse) was more voluble:
Later in the morning, reports of new damage began to appear. @troylivesay wrote: “ More houses and buildings came down in this morning's aftershock. Many more people out in the streets again this am.”  @RAMhaiti added: “ A journalist friend went 2 Carrefour Feuille area after this AM quake;says that what I thought was 1 building falling was several small ones” .
There were also reports of disruption to Internet access, though unclear whether this was caused by the aftershock. @troylivesay remarked “ internet is out” , and @JoyInHope  (a charity organisation in Jacmel) reported: “ AccessHaiti internet out in #Jacmel but we have iChat through satellite with the ground. Info will be slow and spotty today.” 
Bloggers on the ground in Haiti also described the aftershock and its effects on people's nerves. Ellen in Haiti, a Canadian charity worker in the village of Fond des Blancs, wrote :
It's 6:15 am and everyone is out in the yard. We just had a very strong aftershock of 6.0 that lasted about 10 seconds. As usual, our thoughts go straight to Port au Prince where everything is so unstable.
I was sitting at the kitchen table writing emails, and felt it start, expecting another small aftershock. It increased in intensity and didn't stop, so I yelled for Nancy and we ran outside.
People had just started to relax yesterday, working back indoors, sleeping indoors. Now they will be outside again.
BuxmanHaiti, another charity worker in Port-au-Prince, expressed  an anxiety many must have felt:
I am so weary. So afraid this second Earth Quake did more damage and caused more deaths. I am sure the clinic is be very busy today…. This morning during the Earth Quake I jumped out of bed and ran screaming “get out get out” like everyone did not know to do that!
At The Livesay [Haiti] Weblog, Troy Livesay commented :
It was the strongest aftershock we've felt yet. I looked on line and see that they are saying it was a 6.1. I cannot begin to describe how totally afraid everyone here is … these aftershocks stir everything back up to the surface. I would have to imagine that lots of buildings that were hanging close to collapsing may have now collapsed. This aftershock lasted about 15 seconds. The original 7.0 lasted a good 45 seconds. Every time someone opens the front gate (makes a large noise) we all jump to our feet to get out of the house.
But before too long, he reported  on new efforts to bring injured people to the medical clinic his organisation is running. For many people in Haiti, jitters over this morning's aftershock have already been overtaken by the drive to survive and recover from last week's catastrophe.
Global Voices’ Special Coverage Page on the earthquake in Haiti is here .