SEABROOK — Roland Trudeau bent over the trunk of his car, dividing up a long sales slip between himself and his friends. The group had driven to Seabrook earlier that day from Providence, R.I., stocking up for their annual barbecue with a fireworks finale.

The food they can get at home. They came to Seabrook for the fireworks.

After leaving Phantom Fireworks, the group had spent $148, but they were about to make another stop at Fantasy Fireworks nearby to pick up more.

"We do this every year," Trudeau, 24, said. "Last year, we spent $500 or so. We aren't doing that bad so far."

For locals in the Bay State and those from farther away, the trip to New Hampshire to stock up is worth the risk of fines, which in Massachusetts are up to $1,000 if one is caught reselling the fireworks and up to $100 if one is found lighting them off by Massachusetts police.

"Business has been good," said Steve Carbone, owner of Atomic Fireworks on Route 1. "The average family is spending about $100."

At Phantom Fireworks down the street from Atomic, salespeople moved quickly through long lines of customers stocking up for the holiday.

"We were slow at first, but now it's busy," a salesperson said.

The parking lots of fireworks retailers this week were filling with cars with New Hampshire and Massachusetts license plates, as well as vehicles from Rhode Island and Connecticut, where most fireworks are illegal.

A Connecticut man was seen buying fireworks, carrying large cardboard boxes with the help of a store salesperson before loading his SUV and driving away.

Seabrook vendors only need to heed New Hampshire laws, which allow the sales of fireworks and lighting them off on your own property.

But just 15 minutes south, the laws differ. According to Massachusetts law, it is illegal for private citizens to use, possess or sell fireworks in the state or to purchase them legally elsewhere and then transport them into Massachusetts.

The law prohibits any article designed to produce a visible or audible effect. The law also covers fireworks that are sometimes referred to as "safe," such as sparklers, party poppers, snappers, firecrackers, spinners and cherry bombs.

Even these fireworks can cause harm — sparklers burn at 1,800 degrees Fahrenheit, and both Massachusetts and New Hampshire fire marshals warn of the potential injuries that can result when fireworks are in the hands of amateurs.

But with so many people crossing the border in the days before Friday to stockpile supplies for their local barbecues or get-togethers, it is hard to keep track of how many fireworks are transported into Massachusetts illegally.

"The laws are primarily enforced at the local level," said Jennifer Mieth, spokeswoman for the Massachusetts Department of Fire Services. "The state police are very aware of the laws and some of the best enforcement has been during routine traffic stops, where they find out a person has a trunk full of fireworks."

Mieth noted transporting the fireworks in an unsafe manner, such as in the trunk of a vehicle, will automatically result in confiscation and the potential for pricey fines.

Carbone said he does not discriminate against out-of-state customers as long as they are 21.

"We always check IDs and make sure they are 21," he said. "In New Hampshire, we just have to go by our state laws. What they do after they buy them I don't know."

John Raymond, New Hampshire deputy fire marshal, said he does not keep tabs on Massachusetts residents who come into the state to buy fireworks illegally but he does note this time of year is a busy one for his office.

"We get a lot of calls with questions about fireworks," Raymond said. In New Hampshire, firecrackers, bottle rockets and reloadable-type shells are illegal, but other fireworks are acceptable.

Raymond said people buying fireworks in New Hampshire must be 21 years old and adhere to state rules.

"You have to do it on your own property or with the written permission of the property owner, and you can't use alcohol or drugs near the fireworks," he said.