The UN's aid chief has arrived in Yemen's capital, Sanaa, expressing his deep concern about the war-torn country's deteriorating humanitarian crisis.

Mark Lowcock is on his first visit to Yemen since being appointed under-secretary-general and emergency relief coordinator on September 1.

"I have come to Sanaa to have discussions with the authorities and other interlocutors on ways to improve the humanitarian situation in Yemen," he said upon arrival in Sanaa on Wednesday.

Lowcock added his five-day visit to the country was aimed at reaffirming "the strong commitment of the United Nations and partners to alleviate suffering of all Yemenis in need of assistance".

Cholera, malnutrition

Yemen has been devastated by more than two and a half years of war after Houthi rebels captured Sanaa and overthrew President Abd-Rabbu Mansour Hadi's government.

A Saudi-led coalition was formed in 2015 to fight the Houthi rebels and army troops allied with them.

According to the UN, the conflict has killed more than 10,000 people and left over seven million in need of food assistance.

Millions of others do not have adequate access to health, water and sanitation services.

The country has also been hit a cholera outbreak, with 850,000 suspected cases since April.

"I decided to come to Yemen because I am deeply concerned about the humanitarian crisis that has continued to deteriorate," said Lowcock.

His trip to Yemen started on Tuesday with a visit to Aden, the seat of the internationally recognised government, where he held meetings with local officials.

He also met internally displaced people and visited a hospital in Lahj where he met patients receiving treatment for cholera and malnutrition.