Plans to establish a "humanitarian corridor" for Christians and other civilians out of the besieged Syrian town of Aleppo have been slammed by a host of aid agencies.

More than 35 charities and international development organisations shave released a joint statement saying they are "extremely alarmed" at the "deeply flawed" plans.

"A true humanitarian operation would not force the people of Aleppo to choose between fleeing into the arms of their attackers or remaining in a besieged area under continued bombardment," the statement read.

"No one should be forced to flee or remain, and measures must be put in place for the UN to ensure and monitor the safety and protection of anyone voluntarily evacuating."

The charities include a number of Christian organisation such as Christian Aid, Tearfund and World Vision.

They echoed concerns of other activists and said the corridor is a likely precursor for more intensive attacks by government forces, putting those who cannot escape in even greater risk.

The corridor was proposed jointly by the Syrian and Russian governments, who are waging a brutal siege of the city which has been held by rebel forces. With the help of Russian air strikes, Syrian President Assad's forces have trapped around a quarter of a million civilians in the city since last month.

Fighting has intensified in the last few days as the rebels have launched counter offensives to try and break the siege.

It has been reported that chlorine gas was dropped on the town of Saraqeb near Aleppo. It was not clear who was responsible but around 30 people were affected. The attack took place near where a Russian military helicopter was shot down by rebels hours earlier, killing all five on board.

One Aleppo resident told the BBC: "Basic food has completely disappeared. For families who have children, there is no milk in the markets.

"Every day we have at least 20 to 30 attacks by Russian aircraft or by the helicopters.

"There are no cars going around. Public transport has completely stopped because of the lack of fuel. People are staying inside their houses to avoid shelling."

The charities' statement read: "If Russia is serious about averting a humanitarian disaster in Aleppo it should strongly support the UN's call for an immediate weekly 48-hour humanitarian pause to ensure safe, unimpeded and immediate humanitarian access – both for aid to get into Aleppo and for civilians to leave voluntarily.

"As long as the bombing, shelling and fighting continues, and in the absence of any genuine confidence-building measures, civilians cannot be expected to trust in the safety of walking through these proposed corridors."