Manchin was on an out-of-state trip and headed back to the state after hearing about the "horrific blast," he said.
"These are good people, hard working people," Manchin said. "I asked them to do what they do best -- to love each other."
Earlier he sent out a press release, saying he spoke with President Obama, who promised to make every asset available to help.
"Tonight we mourn the deaths of our members at Massey Energy," Massey CEO Don Blankenship said in a prepared statement. "I want to offer my condolences to the miners' families who lost loved ones at Upper Big Branch. And I want to thank the rescue teams and the Massey members who continue to work hard on behalf of our miners and their families."
The disaster comes just four years after a series of mine accidents in West Virginia and Kentucky -- including one that brought criminal prosecution of a Massey subsidiary -- killed 19 workers and prompted the first reform of U.S. mine safety laws in 30 years.
Mine safety experts who were in contact with state and federal investigators said initial reports are that the explosion involved methane that built up inside a sealed area of the mine or that leaked through mine seals.
Such a scenario would be a repeat of the 2006 Sago and Darby disasters in West Virginia and Kentucky, which claimed 17 lives and prompted regulators to take a closer look at the safety of the vast sealed areas of underground coal mines for the first time in years.
"Seals can be deadly if they are not maintained and monitored properly," said Tony Oppegard, a former MSHA staff and longtime mine safety expert from Kentucky.
Outside the Upper Big Branch site, witnesses reported seeing smoke billowing from the mine, and several miners apparently escaped after donning their emergency breathing devices.
More than two dozen ambulances were staged in Whitesville, and crowds of residents lined the streets waiting for word on the potential disaster. Authorities had gathered families of the miners at a Baptist church in Whitesville and at a training building on the mine property, officials said.
"If you're from here, you're part of a coal mining family," said Grace Lafferty of nearby Harper. "You know a lot of people who work here. It takes your breath away, your heart drops and you have that empty feeling."
One miner from the Massey operation declined to give his name, but said, "This is scary in more ways than one."
"We've been through this many times before, and we know West Virginians will band together to get through it, but it doesn't get any easier," Rahall said.
At the 2 a.m. press conference, Rahall said that, though improvements were made after Sago, mine safety laws would have to be looked at again in light of the loss of life on Monday.
"It's unfortunate, but every mine safety law we have on the books today was written in the blood of coal miners," Rahall said. "Obviously, one coal miner's death is one too many."
Margaret White works at the Country General store, just a few miles from the mine.
"I see the men that work there every day. I know what kind of biscuit they want," she said. "I can't believe this happened. They all know me by name, even if I don't know theirs."
Area churches were open throughout the night, cooking food and providing a place for people to gather and pray.
Gary Williams, pastor of the New Life Assembly Church in Whitesville, said he knew many of the miners. At 1 a.m., members of his church were cooking hotdogs to send up to the families and rescue workers.
"We are just as in the dark as you are," said Williams, who works at a different Massey mine. "We are all familiar with them. They're friends we grew up with. Our kids play ball together."
A volunteer wearing a yellow reflective vest walked in the church to pick up the hot dogs.
"I've got hungry rescue workers up there, hungry families, hungry medical examiners," she said.
The Upper Big Branch Mine-South employs about 200 workers and last year produced about 1.2 million tons of coal, according to company disclosures filed with MSHA.
In seven of the last 10 years, the mine has recorded a non-fatal injury rate worse than the national average for similar operations, according to MSHA statistics.
Between 2008 and last year, safety violations at the operation more than doubled and fines issued by MSHA tripled, according to agency records.
One miner was killed at the operation in a July 2003 electrical accident and another in a March 2001 roof fall, according to MSHA records.
In January 2006, two miners died in a fire at Massey's Aracoma Alma No. 1 Mine. Eventually, Massey's Aracoma Coal Co. subsidiary pleaded guilty to 10 criminal mine safety violations and paid $2.5 million in fines related to that fatal fire.
On its corporate Web site, Richmond, Va.-based Massey says that in 2009, the company recorded "an all-time best" non-fatal accident rate and was the "6th consecutive year and the 17th year out of the past 20 years in which Massey's safety performance was stronger than the industry average."