PARIS - A huge manhunt for two brothers suspected of massacring 12 people in an Islamist attack at a satirical French weekly zeroed in on a northern town Thursday after the discovery of one of the getaway cars.

Meanwhile, Paris said the highest alert level has been extended north to the region where the attack suspects were spotted.

The men, believed to be brothers Cherif and Said Kouachi, are reportedly holed up in a house in Crépy-en-Valois, north-east of Paris, Daily Mail reported. But other reports put them in the neighbouring town Villers-Cotterets.

Bruno Fortier, the mayor of Crépy-en-Valois, said helicopters were circling his town and police and anti-terrorism forces were deploying en masse.

"It's an incessant waltz of police cars and trucks," he told Reuters, adding that he could not confirm reports the men were holed up in a house in the area.

The Telegraph reported that the men were spotted in the woods outside Villers-Cotterets. Their photographer has spoken to a man who was warned to leave a local restaurant "because the police were coming", the paper said.

The restaurant owner said that he had been told "two armed men are in the woods". The Foret de Retz is said to be 13,000 ha - larger than the size of Paris, which is 11,000 ha, The Telegraph said.

BBC reports that police have blocked the road running from the N2 highway to another neighbouring village - Longpont.

The discovery of their getaway car, abandoned in the northern town of Villers-Cotterets, was a breakthrough in the frantic police hunt.

RAID, the anti-terrorist unit of the French police force, and the GIGN, a paramilitary special operations unit, were deployed in Villers-Cotterets in the northern Aisne region on Thursday "where a car was abandoned after being used by the two suspects, who were identified by a witness", a source told AFP.

Cherif, a militant well-known to police, and his brother Said, were spotted by the manager of a petrol station in the town about an hour's drive north-east of Paris. The manager, who was robbed by the duo, identified the two men, said reports. Some reports also claimed they fired shots.

This came as reports said that French investigators found a dozen Molotov cocktails and two jihadist flags in the getaway car used in the massacre at a Paris magazine.

"This shows their Islamist radicalisation and that they had possibly planned other acts with the petrol bombs," a source close to the case told AFP.

The items were found in the abandoned black Citroen used by the attackers to speed away from the offices of the Charlie Hebdo.