United Nations, UN Secretary-General Antonio Guterres is deeply concerned about the condition of the Safer oil tanker moored off the western coast of Yemen and has asked for access to the vessel for its assessment, his spokesman said.

The UN chief urges the removal of any obstacles to the efforts needed to mitigate the dangers posed by the tanker without delay, Xinhua news agency quoted Stephane Dujarric as saying on Friday in a statement.

Guterres specifically calls for granting independent technical experts unconditional access to the tanker to assess its condition and conduct any possible initial repairs.

This technical assessment will provide crucial scientific evidence for next steps to be taken in order to avert catastrophe, said the statement.

The aging tanker has had almost no maintenance since 2015 and risks causing a major oil spill, explosion or fire that would have catastrophic environmental and humanitarian consequences for Yemen and the region.

The Houthi rebels, who control the territory where Safer is moored, first indicated on July 5 that they would allow an inspection and emergency repair team to board the floating oil storage and offloading vessel.

An official UN request was sent on July 14 and the world body is still waiting for permission from Houthi rebels.

On May 27, seawater leaked into the engine room, threatening to destabilize and sink the entire vessel, and potentially releasing all the 1.1 million barrels of crude oil into the sea.

A temporary fix by divers from the Safer corporation succeeded in containing the leak.

But the fix is unlikely to hold for very long, warned the UN.

An oil spill would have catastrophic environmental and humanitarian consequences, including destroying livelihoods and shutting down Hodeidah port, a vital lifeline for millions of Yemenis who depend on commercial imports and humanitarian aid.

The tragic Beirut explosion on August 4 and the recent alarming oil spill in Mauritius from a Japanese bulk carrier demand the world's vigilance and urgent action to avert preventable loss of life and livelihoods where possible, said the note to correspondents.

Research by independent experts indicates that an oil spill from Safer could destroy Red Sea ecosystems on which almost 30 million people depend, including 1.6 million Yemenis.

All the fisheries along the Yemeni west coast would be impacted within days and the livelihoods of the fishing communities would collapse, at a time when 90 per cent of these populations are already dependent on humanitarian aid, it said.

An oil spill could lead to the closure of the key port of Hodeidah for up to six months.

Experts estimate that a six-month closure would increase fuel prices in Yemen by 200 per cent for months, double food prices and hinder the delivery of vital humanitarian aid to millions of Yemenis.

Other Red Sea littoral countries, including Djibouti, Eritrea and Saudi Arabia, would suffer as well.

A spill could also debilitate one of the world's busiest commercial shipping routes through the Red Sea, which accounts for about 10 per cent of global trade.

Overall, the impact of an oil spill from the Safer tanker would cost an estimated $1.5 billion over 25 years.

If fire erupts on Safer for any reason, more than 8.4 million people would be exposed to harmful levels of pollutants.

The government of Yemen and the Houthis first approached the UN to provide support in resolving the Safer tanker issue in early 2018.

But the escalation of military hostilities on the Yemeni west coast throughout most of 2018 made safe access to the tanker impossible.

In 2019, both Yemeni parties approved the deployment of a UN technical team to assess the damage and conduct any feasible immediate repairs.

The Houthi authorities granted the UN the travel authorizations to come to Hodeidah but did not provide the final clearances necessary to access the tanker by sea.

Since then, the UN has repeatedly attempted to obtain the required authorizations to deploy the expert team.