Earlier, police had chased a vehicle at high speed along the nearby A2 motorway towards Paris as authorities appeared to be closing in on the two brothers. Gunshots rang out and police trucks, ambulances and armoured vehicles descended on the area close to Paris's Charles de Gaulle airport.
Police and anti-terrorist forces blocked all entries to the town of about 8,000, clearly seeking to limit the scale of any siege.
"All residents are requested to remain at home. Children are to be kept safe in school," the municipal website said.
The danger of hostage taking or of a second attack has been a central concern of security services since the gunmen stormed the Paris offices of the satirical weekly newspaper Charlie Hebdo on Wednesday, killing ten journalists and two police officers.
Interior Ministry spokesman Pierre-Henry Brandet told iTELE television he was fairly sure the two suspects were in the building currently surrounded.
"We are almost certain it is those two individuals holed up in that building."
Yohann Bardoux, a plumber whose office is two doors down from the printing shop where the hostage drama is taking place stayed away from work after hearing gunfire. But he said his mother was in the building next door to the printing shop.
"Of course I'm worried about her, I hope it all comes down soon, and turns out well," Bardoux said.
"They are everywhere. It's really jumping. They've blocked the whole zones, we've got helicopters overhead, the police presence is impressive."
A senior Yemeni intelligence source told Reuters one of the two suspects, French-born sons of Algerian-born parents, was in Yemen for several months in 2011 for religious studies; but there was no confirmed information whether he was trained by Al Qaeda in the Arabian Peninsula (AQAP).
The gunmen shouted "Allahu Akbar" (God is greatest) as they carried out the attack, which has been described by President Francois Holland and other world leaders as an attack on the fundaments of democracy.
The weekly newspaper appears to have been targeted because of its lampooning of Islam and cartoons of the Prophet Mohammad.
The fugitive suspects are both in their early 30s, and were already under police surveillance. One was jailed for 18 months for trying to travel to Iraq a decade ago to fight as part of an Islamist cell. Police said they were "armed and dangerous".