International aid groups on Wednesday appealed for safe passage for civilians in Yemen, as a battle between rebels and government forces nears one of the country's most densely populated cities.

The UN children's fund (UNICEF), the International Committee of the Red Cross (ICRC) and Doctors Without Borders called for the protection of civilians in the Red Sea port city of Hodeida, as clashes approach civilian hospitals.

"We at ICRC are worried about civilians and civilian infrastructure in Hodeida," said ICRC spokeswoman Mirella Hodeib.

One of the biggest hospitals in Hodeida, Al-Thawra, is now only "metres away from an active frontline", she added, speaking from the Yemeni capital.

"We're talking about dying children who are currently at the hospital," said UNICEF spokeswoman Juliette Touma.

"What we are fearful about is that the escalation of violence is highly likely to jeopardise humanitarian efforts that are life saving," she told AFP.

"We need to be able to continue to deliver humanitarian assistance, because if we are not, the dire humanitarian situation in Yemen is likely to become even worse."

Doctors Without Borders (MSF) on Wednesday announced it had suspended its work in the Daleh region east of Hodeida.

"There have been multiple security incidents directly targeting patients, staff and MSF-supported medical facilities in the area. We are left with no choice but to close all activities in Daleh governorate," said Ton Berg, the group's head of mission in Yemen.

The most impoverished country in the Arab world, Yemen has been gripped by war since 2015, when a regional military coalition led by Saudi Arabia joined the government's fight against Iran-backed Huthi rebels.

The pro-government coalition drove the Huthis out of a string of ports they had seized, but the rebels still control the capital Sanaa as well as Hodeida.

The coastal city is home to Yemen's most valuable port, crucial for nearly 80 percent of aid deliveries and food and fuel imports into the war-torn country.

The port has been under blockade by the Saudi-led alliance for a year, a move the coalition says aims to curb the smuggling of weapons from Iran to the Huthis.

Tehran denies it arms the rebels.

Nearly 10,000 Yemenis have been killed since 2015, according to the World Health Organisation, and the country now stands on the brink of famine.