A close friend of the man behind the popular Ice Bucket Challenge drowned in Massachusetts on Saturday morning, hours after the campaign reached $100,000 in fundraising.

Corey Griffin, 27, was friends with Pete Frates, the man who inspired the Ice Bucket Challenge after being diagnosed with ALS.

Griffin was a key supporter of Frates' mission to find a cure for the disease also known as Lou Gehrig’s, a Facebook post by Frates said.

According to the Nantucket police, emergency responders were called after a man was seen diving from a building into the harbour below.

Witnesses saw Griffin dive from the Juice Guys building into the water at about 2 a.m., police said. Griffin floated to the top at first, but then he went under again and did not resurface.

A Nantucket lifeguard rescued Griffin from the bottom of the harbour and police gave him CPR and transported him to the hospital, but efforts were unsuccessful.

Griffin was officially declared dead at 3 a.m.

In a Facebook post on Saturday, Frates wrote a few words about his friend.

"Helping out was nothing new for Griff. He held his own event for me back in 2012, just a few months after diagnosis," Frates wrote. "He worked his butt off these last few weeks for ALS.

"Team FrateTrain lost a good friend today."