IMO secretary-general Kitack Lim is again calling for action on the worsening crew change crisis keeping hundreds of thousands of seafarers on board their ships with no relief in sight.

In at least the fourth time Lim has requested action from world governments on the issue, the head of the global regulator told the United Nations' General Assembly that the estimated 300,000 seafarers working currently "cannot remain at sea indefinitely".

"Nearly six months have passed since Covid-19 was declared a pandemic, and the numerous restrictions and obstacles that prevent crew changes have created a humanitarian crisis at sea," Lim said.

"If the crew change crisis is not resolved soon, ships will no longer be able to operate safely pursuant to the organisation’s regulations and guidelines, further exacerbating the economic impacts of the Covid-19 pandemic."

The Covid-19 pandemic has jurisdictions around the globe reticent to allow seafarers to disembark and be replaced, concerned they could spread the respiratory illness that has already killed more than 800,000 worldwide.

Meanwhile, some seafarers have been working for nearly 18 months. Others are stuck shoreside without work.

In his note, ahead of the General Assembly's 75th session set to kick off next Monday, Lim said seafarers have been "nothing short of heroic".

The latest statement follows May's publication of a 12-step plan to facilitate crew changes, Lim's request for "key worker" status in June that would designate their work essential and a 26-point plan in July to help get injured seafarers stuck aboard their ships medical treatment.

The past overtures appear to have fallen on deaf ears, although the IMO insists after "numerous top-level statements" and diplomatic meetings, that "significant progress has been made" albeit not fast enough.

Lim's most recent comments again call for "key worker" status, which has the support of UN secretary-general Antonio Guterres, and the implementation of the 12-step crew change framework.

Instead of the usual General Assembly session, which sees global leaders descend on New York in an effort to talk through the world's issues, most will opt to appear virtually.

During the session, the IMO, the International Labour Organization and the UN Global Compact will hold a side event on 24 September to bring attention to the crew change crisis.