New Kids on the Block singer Joey McIntyre had passed the finish line at the Boston Marathon just “minutes” before the horrific explosions that left at least two dead and more than 100 injured.

One of the dead has reported to be an eight-year-old boy. At the time of writing, doctors at three nearby hospitals have carried out 10 amputations between them and are pulling out ball bearings from wounds. Seventeen people are in a critical condition, and approximately 130 injured.

The 40-year-old pop star had been among the estimated 27,000 runners to participate in the marquee marathon Monday.

But two massive blasts occurred about 15 seconds apart near the finish line at Boston’s Copley Square around 2:45pm.

In the aftermath of the early news reports, NKOTB bandmate Donnie Wahlberg took to Twitter to frantically ask for information on his friend’s whereabouts.

Wahlberg tweeted: "“Please reach out if you hear that @joeymcintyre is ok!!!!! Please say a prayer for everyone in Boston!"

McIntyre responded after the blast to let family, friends and family know he was safe.

“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,” McIntyre tweeted.

McIntyre was running in the marathon to raise money and awareness for the Alzheimer’s Association and in memory of his mother who suffers from the disease. He tweeted a photo once he crossed the finishing line (see below).

Elsewhere in Twitter artists, bands and their fans have all expressed their shock on hearing about the bombings. Ed Sheeran, One Direction's Zayn Malik, Rob Kardashian and Stooshe tweeted out the hashtag #PrayForBoston

Cheryl Cole tweeted: "Sickened and saddened!! Thoughts go to everyone affected in Boston !! Stop this world. I want off #PrayforBoston".

The Wanted tweeted: "Our hearts go out to all those who are affected by this senseless tragedy #prayforboston".

Google has activated its Person Finder service in the aftermath of the Boston Marathon explosions.