Morning in Boston and heady anticipation as thousands prepared for the Boston Marathon: 

T minus 5 minutes!!!! http://pic.twitter.com/wD7iPKqbV6Joey McIntyre

Four hours later, as many were crossing the finish line…

There was an explosion by the finish line about 5 minutes after I finished- I’m ok but I’m sure there are many hurt.Joey McIntyre

Thoughts & prayers to everyone that was near the explosion by the Boston Marathon finish line. scary #BostonMarthon pic.twitter.com/59qJXBl6NWTeam Runner For Life

In the midst of chaos, many were trying to reach family and friends:

Keep passing people making the "Mom, I’m safe" phone call.Billy Baker

I’m okay, guys. My dad ran the Boston Marathon 5k yesterday, so that’s when we were in that area.… instagram.com/p/YJLRsVOO4V/T a y l o r

I’m am okay my family and teammates are okay. Please please pray for those who were running and got hit by the bomb. Pray 4 family’s-friendsTatyana McFadden

Shockwaves from Boston around the world. http://twitpic.com/cjn90mJonathan Wald

Canadian Paralympian Josh Cassidy was excited to attempt a repeat his 2012 Boston Marathon win, where he set a record for fastest time ever by a person in a wheelchair.

2moro is the big day @jhboston26 #BostonMarathon! Biggest+best field 2date! In better shape this yr but forecast headwind.Shld b intersting!Josh Cassidy

But his 2013 race will carry different memories.

Just letting everyone know I’m okay. Was across the street from the finish line explosions outside my hotel. Thank u all for the mssgs xoJosh Cassidy

To get the word out, many used Twitter as a way to tell loved ones they were safe.

In downtown Boston. I’m okay! This is madness. PrayingTy Rimmer

Bombs went off like a mile from us. Can’t believe this is happening.Ty Rimmer

Scary day to be in Boston. I’m okay though – to everyone asking.Kyle VanZandt

I was in Boston today but I’m all good. Thanks to everyone who reached out to me. I’m okay so that’s what matters I suppose #prayerstobostonJosh

Thank you twitter friends for checking on me. I’m home safe but we really need to pray for those involved #prayforbostonJules

Going to bed happy in the knowledge that my uncle Bobby is safe in #Boston #blessed Thinking of everyone there. X http://pic.twitter.com/OfpJIvZq1rZara King

texts are not going through – but i’m okay and so are friends/coworkers who were runningMolly Wasser

A picture of my cousin, on the left, he ran in the Boston marathon today, I’m glad he is safe! #bostonmarathon pic.twitter.com/vSqlIS4fvhBen Knockleby

i’m okay, was 3 miles away from finishing but scarred for life and probably not running a marathon againNate MacDonald

Everyone need to get out of the Boston Marathon Area because it’s not safe. Please tweet or share this—> http://pic.twitter.com/k7bX22dkyacatching is fire

I’m fine and safe, friends. Just heartbroken. #Boston #fbEmily Keller

I’m okay everyone!! View outside of my hotel right now! #crazy #BostonMararthon http://pic.twitter.com/gZwu6dTmBlandrew cecil

I’m am okay my family and teammates are okay. Please please pray for those who were running and got hit by the bomb. Pray 4 family’s-friendsTatyana McFadden

From NewsChannel5’s Chris Conte, who ran the Boston Marathon today: "Ok everyone I’m fine. The two explosions… fb.me/2q7biwSJ4NewsChannel 5

Serious tweet for once. I’m getting a lot of texts as some of you know I’m in Boston at the moment. I’m fine,place is in chaos, though.Chris Greene

I’m okay. "@mitchdeyoung: @KathyReports just thinking of all my Boston people. Are you okay? Lots of good … http://m.tmi.me/SjYOuKathy Curran

Not everyone made it out okay, however. The Boston Herald says at least three are dead and more than 100 are injured. The hashtag #prayforboston will continue to trend.

The Boston Marathon was in honor of the Sandy Hook School shooting, I’m speechless… just prayers. #PrayForBoston pic.twitter.com/STqqR8IUKpEd Sheeran

I’m sadden to hear bout Boston. Thoughts and prayers go out to all those affected. Be safe everyone! ? http://pic.twitter.com/U53KgYAK7M Honey

#prayforboston instagram.com/p/YJTJJaJqH3/Emie Yokokura

Pray for Boston http://pic.twitter.com/e6uxF1keNWSEALofHonor

Pray For Boston http://pic.twitter.com/lBgyEvRC6sMatty Young

RT @julianawijaya: #prayforboston http://twitpic.com/cjndksCHRISTY ANGKA

Don’t stop retweeting. This is a sick world we live in.. #prayforboston pic.twitter.com/qJeTis6VEQEarth Pics