Braving Syrian army patrols and treacherous winter weather, hundreds of people fled into Lebanon in the last 24 hours to escape the heaviest shelling of their border towns in a year-long crackdown on protests against President Bashar al-Assad, Reuters reported.

In the hillside town of Arsal in Lebanon's Bekaa Valley, residents say between 100 and 150 families arrived from Syria on Sunday, March 4 - one of the biggest refugee influxes so far.

A dozen families spent Sunday night in a three-storey apartment block in Arsal after fleeing what they said was a sustained army attack on the Syrian town of Qusair with tanks, rocket-propelled grenades and helicopters.

Families trekked on foot through snow-capped hills to safety, but many others were caught as they tried to flee, one refugee said.

Only a few families, of roughly 2,000 people who fled Qusair, made it across the border without being stopped by Syrian troops.