Yemeni forces backed by a Saudi-led coalition have launched a major offensive to retake the rebel-held port city of Hodeida, despite UN warnings of a "catastrophic humanitarian impact".

Field commanders said that troops pushed towards Hodeida airport after Yemeni pro-government forces received a "green light" from the coalition. The offensive is controversial because the port serves as the entry point for 70 per cent of Yemen's imports as the country teeters on the brink of famine.