Turkish artillery fire on the Kurdish-majority enclave of Afrin in northern Syria killed at least 18 civilians on Friday, a monitor said.

"There is fighting on the northern edge of the city," the Britain-based monitoring organisation said.

On January 20, Turkey and Syrian Arab rebel proxies launched an air and ground offensive on the Afrin region, which is controlled by the US-backed Kurdish People's Protection Units (YPG).

Ankara has consistently denied targeting civilian infrastructure but the Observatory said at least 245 civilians, including 41 children, have been killed in less than two months.

Turkish-led forces have nearly fully encircled the city of Afrin, with only one road left open for civilians to flee to areas controlled by the Syrian regime or the YPG.

The Observatory said on Thursday that more than 30,000 civilians had fled Afrin in 24 hours.