The cause of a fire at World Pie restaurant in Bridgehampton remained under investigation yesterday, four days after the blaze closed down the mainstay at the start of the busy Memorial Day weekend.The Bridgehampton Fire Department was called to the restaurant at 2402 Montauk Highway, part of Bridgehampton’s Main Street, at 9:24 a.m. on Saturday. Police and firefighters confirmed that there was a fire in the restaurant’s dining area on the west side of the building. Montauk Highway was shut down between School Street and the Bridgehampton-Sag Harbor Turnpike to accommodate the engines.Chris Hansen, the Southampton Town fire marshal leading the investigation, said the fire began underneath the dining area in a crawl space that is open on three sides. It was used for the storage of outdoor umbrellas and similar items, but Mr. Hansen said he wouldn’t classify it as a storage area.“Right now, I’m not pointing a finger at anything yet,” he said, adding that the fire was not suspicious. “It’s still under investigation.”The fire was initially extinguished, but around 9:50 a.m. firefighters reported seeing flames in the basement underneath the older part of the building. The fire chiefs then requested the Southampton Fire Department to assist and asked for an engine from the Sag Harbor Fire Department to stand by at Bridgehampton’s headquarters. A rapid intervention team from the East Hampton Fire Department was called in as well.No one was hurt. The restaurant hadn’t yet opened for the day when the fire broke out.Though the flames were quickly extinguished, there was an extraordinary amount of heat, and firefighters discovered more fire behind walls and in the ceiling of the basement, according to Bridgehampton Fire Chief Gary Horsburgh. They had to cut holes in the floor in the dining area to vent the fire in the basement. “The floor by the bar started to give way, so we had to cut that to vent it.”“It’s pretty bad,” Chief Horsburgh said of the fire and smoke damage that afternoon. “It’s going to be a while before he’s up and running,” he said of the owner, Michael Mannino. “I felt sorry for him — it’s Memorial Day weekend. It was sad, really, cutting the guy’s place up, but we had to do it.”The good news, Mr. Hansen said, was that there was no structural damage to the building.On World Pie’s Facebook page on Sunday a note was posted to customers that indicated the restaurant could reopen late next month. “Thank you to everyone who showed your support and concern Saturday morning after a spark ignited in the basement,” the note said. “We are planning to be up and running in about three weeks with a celebratory reopening.”The restaurant will need approval from the Suffolk County Department of Health Services before reopening.Rowdy Hall in East Hampton went through that process just last month when an outdoor refrigeration unit at the restaurant malfunctioned. While the building next door, which housed a J. Crew clothing store and a few offices, suffered most of the damage, Rowdy Hall had to close for repairs. Just two weeks later, it managed to reopen, with a thank-you party for the emergency workers who responded.