Bulgaria is facing a backlash from human rights groups after building a 30km-long, razor-wire fence along its southern border in an effort to block immigrants coming in from Syria via Turkey.

The 3m-high fence, which has taken a week to build and was completed on Thursday, has already reportedly brought the number of illegal arrivals down to 300 per month compared with 2,000 people each month this time last year.

Bulgaria was caught unprepared by a surge of 11,600 Syrian, Turkish and Afghan refugees last year following the crisis in Syria - 10 times the annual number of asylum seekers to the country before the civil war.

The sudden influx caused a humanitarian crisis in Bulgaria, already the poorest member of the EU, as asylum seekers were forced to live in crowded army barracks and tents during the middle of winter with no heating, basic sanitation or food.

The fence, which covers the least visible section of Bulgaria's 275km border with Turkey, has come under fire today from human rights groups.

Bill Frelick, refugee rights program director at Human Rights Watch said: "Slamming the door on refugees is not the way to deal with an increase in people seeking protection.

"The right way, simply, is for Bulgarian authorities to examine asylum seekers' claims and treat them decently."

A recent report by Human Rights Watch detailed how Bulgarian border police have this year used excessive force to return people who appear to be asylum seekers back to Turkey with no opportunity to lodge asylum claims.

Human Rights Watch interviewed 177 refugees, asylum seekers and migrants in various locations in both Bulgaria and Turkey. Those interviewed gave detailed accounts of incidents involving at least 519 people in which Bulgarian border police apprehended and returned them to Turkey, in some instances using violence.