Firefighters have kept a vast wildfire in southwest France from advancing overnight, extinguishing flare-ups near Atlantic coast dunes before returning heat and drier air threatens to test their hold on the blaze

LEGE-CAP FERRET, France — Firefighters kept a vast wildfire in southwest France from advancing overnight Tuesday, extinguishing flare-ups near Atlantic coast dunes before returning heat and drier air threatened to test their hold on the blaze.

The fire remained stabilized at 6 a.m. after a calm night and the burned area was unchanged at 420 square kilometers (162 square miles), the Gironde prefecture said.

Several flare-ups were detected overnight north of Le Porge and in dune land north of Cap Ferret but were brought under control by firefighters, authorities said.

The areas lie along the Atlantic coast west of Bordeaux, where crews have battled the blaze since it erupted near Saumos last week.

The blaze, raging since last week, has been wildly unpredictable, transforming at times into a self-feeding fire storm as it burned through an area four times the size of Paris and forced 220,000 people to flee their homes.

Although its advance has been halted, officials have repeatedly cautioned that smoldering vegetation and falling humidity could trigger fresh outbreaks.

Firefighters and military engineers resumed work early Tuesday on tactical firebreaks designed to prevent the flames from spreading. Authorities said 103 kilometers (64 miles) of barriers had been created.

Ninety-three firefighters have been injured during the operation, the prefecture said.

A section of the A63 highway remained closed, while rail traffic south of Bordeaux was suspended except on the route toward Toulouse.

The cautious progress in Gironde came as thousands of people began returning home after a separate wildfire in the neighboring Landes region displaced more than 30,000 residents and vacationers.

French President Emmanuel Macron said Monday evening that the Landes fire had been contained.