French counter-terrorism police have surrounded an apartment in Paris after a known extremist armed with a knife allegedly barricaded himself inside the property.

The man holed up inside the building is reportedly known intelligence services for his links to ISIS and may have previously travelled to Syria.

A family member of the suspect contacted the police, informing them that the man is carrying a knife and has locked himself inside in the building.

A police source has told French media that the man is understood to have psychiatric problems and his family have previously tried to persuade him to seek professional help.

The man holed up inside the building is reportedly known intelligence services for his links to ISIS and may have previously travelled to Syria

It is understood that the man is believed to have a psychiatric disorder and may have previously refused medical treatment

The man has not been named, but has reportedly been 'in the process of radicalisation', according to the Daily Star.

The dramatic scenes comes after four suspected extremists were detained by police in the Belgian city of Antwerp.

The four suspects were accused of collecting money to buy arms and explosives as well as developing plans to attack Antwerp's main train station.

Belgian prosecutors have said all four suspects have been charged with participating in the activities of a terrorist group, but declined to give additional details.

The man's father is understood to have alerted authorities, who rushed to the apartment in Paris

The man has not been named, but has reportedly been 'in the process of radicalisation', according to the Daily Star

130 people were murdered in the devastating terror attacks on the streets of Paris in November 2015

The suspects were reportedly exchanging encrypted messages with other Belgians in Syria including Hicham Chaib, a leading figure of ISIS in its Syrian stronghold of Raqqa.

The broadcast says it was those communications that worried Belgian authorities, who detained the suspects Wednesday as well as a number of minors following searches in the Antwerp area.