LAWRENCE — The federal government has declared the city block that burned this week a disaster area, making businesses, homeowners and renters eligible for financial help.

Mayor Michael Sullivan said he received word yesterday of the decision that makes loans of up to $1 million available for businesses that received heavy damage in the blaze, which happened early Monday morning, destroying nine buildings.

Homeowners can use low-interest loans to borrow a maximum of $200,000 and renters could receive up to $40,000 in disaster relief assistance if their claims are approved by the federal Small Business Administration.

In addition, the city and individuals suffering heavy financial losses from the fire could receive reimbursement from the Federal Emergency Management Agency.

Federal officials were expected to set up a temporary office Tuesday in the main branch of the Lawrence Public Library. There, people who lost property in the fire can apply for low-interest loans. The federal government will have bilingual staff available to assist victims in filing their claims.

“This is great news for property owners and victims of this tragic fire,” Sullivan said last night. “This is a major part of the rebuilding process. What’s really amazing is that it took just one day for the federal government to approve this.”

This is the second time in as many years that the federal government has declared part of Lawrence a federal disaster zone. Parts of the city met the same designation in May 2006 after the Mothers Day floods. Sullivan said it took about a week for federal officials to approve the city’s request back then.

Investigators are gathering information about the South Lawrence blaze, but say it will be a week before they can determine the cause. They were scheduled yesterday afternoon to interview tradesmen and a construction supervisor who were working on renovations at the former Millennium nightclub at 34-44 Parker St., where the early-morning blaze began, they say.

Already, investigators have dug through the rubble of what was to be a restaurant, but the search yielded few solid clues.

“They call these a ‘black-hole’ fire,” city fire Capt. William Lannon said, describing the remains of the nine residential buildings — two of which had commercial space — as looking like the remnants of a war zone.

“It’s almost like archaeology,” he said of digging through the rubble for clues.

The search did turn up portable propane and kerosene-fueled heaters known as salamander heaters. Those were supposed to be removed last week after a Jan. 18 surprise city inspection found one being used without a permit, fire officials said. Building owner Geraldo Torres of Methuen said the heater was shut off immediately after the inspection.

To qualify for the federal disaster designation, the city had to show that at least 25 homes and businesses received significant losses and that at least 40 percent of that loss was uninsured. Sullivan said last night that city officials figure the property damage alone surpassed $4 million, which included nine buildings that were destroyed.

“When you consider that 38 apartments were destroyed and other units are not livable now, there are probably up to 180 people who have been displaced from their homes,” Sullivan said.

“With probably three or four people to an apartment, you could run as much as $5,000 per apartment to furnish. You could have $5 million as far as claimable reimbursements. There were six or seven vehicles that were destroyed by the fire,” the mayor said.

The city incurred more than $200,000 in overtime costs related to the fire — expenses that could also be reimbursed by the federal government.

Relief efforts were happening yesterday to provide clothing and furniture to families who lost their homes in the blaze. More than 20 volunteers from the YouthBuild Lawrence organization spent the day cleaning empty rooms in the no-longer-used Saunders School on South Broadway. The school will serve as a donation center.

“That’s going to be headquarters for all the donations so people who were affected by it really won’t have to travel all over to different places looking for it,” said Mikey Caban of YouthBuild.

Monday’s fire broke out around 2:30 a.m. inside the former nightclub, which is at the corner of Parker and Market streets, investigators believe. It then spread east on Market Street, taking out a row of homes, and south on Parker Street, burning down a large building that held a grocery store and apartments.

In all, five occupied buildings and four being prepared for occupancy were destroyed, fire Chief Peter Takvorian said. Counting garages, sheds and homes that sustained damage brings the number of affected buildings to 14.

The mayor credited this week’s quick response this time to collaborative work and lobbying efforts by Gov. Deval Patrick, the state legislative delegation, U.S. Sens. Edward Kennedy and John Kerry and Congresswoman Niki Tsongas. They all sent letters to federal officials requesting disaster help.