A dramatic three-alarm fire in the center of Provincetown over the holiday weekend shuttered several restaurants along the waterfront indefinitely, just as the summer tourist season begins.

“Right now, people are in shock,’’ said Cheryl Andrews, chairwoman of the town’s Board of Selectmen. “They are in for a rough summer.’’

The fire started at about 6 p.m. Saturday in the ventilation system of a deep fryer used in the Red Shack restaurant in Lopes Square, Andrews said. The restaurant is known for its lobster rolls.

Flames and smoke were soon billowing from the roof of the building on Commercial Street at the foot of MacMillan Pier, where ferries from Boston and Plymouth bring thousands of visitors to town each summer. The fire was so intense that witnesses spotted smoke from across Cape Cod Bay.

With help from neighboring towns, Provincetown’s volunteer firefighters brought the blaze under control within hours and stayed through the night to make sure flames did not flare up again. The fire hoses were disconnected at 9:45 p.m., according to the American Red Cross of Massachusetts. No injuries were reported.

But damage to the charred building was so extensive that it was unclear when the Red Shack and two other restaurants in the building — the Surf Club Restaurant and Tatiana’s Foot Long Hot Dogs — could reopen. A fourth restaurant in a building next door, the Coffee Pot, was forced to close temporarily.

Laurie Probstein, 46, of Brookline, said she has been eating at the Red Shack for roughly two decades and viewed the aftermath of the fire on Saturday night and again on Sunday. She said people were taking pictures of the charred remains on Sunday.

“It’s so sad,’’ said Probstein, who works in information technology and was visiting Provincetown with her family. “We found what was left of the block.’’

Probstein said the Red Shack was “gutted’’ and Tatiana’s looked “horrible.’’ She said the damage appeared more limited at the Coffee Pot and Surf Club. “The Surf Club looks like it is likely going to be OK, but clearly there is some water damage,’’ she said.

The timing is particularly tough because many restaurateurs and retailers in the area rely on the busy tourist season for the lion’s share of their incomes for the year.

State Fire Marshal Peter J. Ostroskey said his office was working with local officials to determine the cause, but said it was too early to know. “That remains under investigation,’’ he said. The Provincetown Fire Department did not respond to calls and e-mail.

Leonard Enos, the owner of the building, told the Cape Cod Times on Saturday that the fire was “catastrophic.’’ He said many of his seasonal employees had just started working on Saturday. “It’s not the way to start, I’ve got to tell you that,’’ he told the newspaper, while huddling with workers outside the building. Enos did not return calls on Sunday.

The structure — not including the land — was valued at $1.3 million, according to town property records.

Still, business owners and residents said they were thankful the blaze was not worse.

When Donald Coill saw photos and video of the fire on the Internet Saturday night, he feared the blaze would wipe out nearby structures, including his own.

“I figured there would be no building in the morning,’’ said Coill, whose company owns the property next to the building that houses the Red Shack. “I figured the whole corner was going to be gone.’’

But Coill said his building suffered only minor roof damage, as well as water damage inside. One of his tenants, a shop called the Lily Pond, had reopened by Sunday morning. And another, the Coffee Pot, could reopen within a week, said Roberta Annese, a volunteer at the Provincetown Chamber of Commerce. Annesse said other buildings on the street were unaffected.

“Everything is open as usual, and people are happy,’’ Annese said.

Town residents feel lucky the fire did not spread farther, Annese said. She noted that the street is dominated by old wood-frame buildings that could have succumbed to a wilder blaze. “If the winds had been worse, there would have been the possibility of losing the whole block,’’ she said.

Both Annese and Coill praised Provincetown’s volunteer firefighers.

“They must be one of the best volunteer fire departments in the country,’’ Coill said.

Fire departments from other towns on the Cape helped douse the flames, including units from Brewster, Eastham, Harwich, Truro, and Wellfleet.

Andrews said the damage to the building where the fire started looked “pretty serious.’’ She said it will be up to the building inspector to decide whether the building can be repaired.

Regardless, Andrews said she is confident residents will find a way to help the business owners and workers survive the losses.

“This town takes care of its people,’’ she said.

Todd Wallack can be reached at twallack@globe.com. Follow him on Twitter @twallack.