Cyclone Chido barrelled into the archipelago at the weekend, leaving health services in tatters, power and mobile phone services knocked out and the airport closed to civilian flights, while there is mounting concern about how to ensure supplies of drinking water.

The French Red Cross said it had 300 volunteers and 137 employees in Mayotte.

"Since the cyclone, due to communication breakdowns and power cuts, (the French Red Cross) has been struggling to reach them. To date, it has been able to contact 70," a spokeswoman told AFP in an email.

The fact that many were so far unaccounted for "does not mean at this stage that they are missing", she stressed, adding that efforts to reach the rest were being stepped up.

The Geneva-based International Federation of Red Cross and Red Crescent Societies, which comprises the French Red Cross and 190 other national societies, had earlier warned that many Red Cross volunteers were missing.

"We are talking about more than 200 volunteers already affected and ... missing," IFRC spokesman Tommaso Della Longa told BBC television.

"They don't have any contact with them."

He said that "French Red Cross colleagues already deployed some teams and some humanitarian aid before the cyclone hit.

"But then of course, being prepared for such a heavy impact is very complicated," he said, describing the logistics as "a nightmare".

Della Longa warned that "even shelter is lacking at the moment, and then you need to organise distribution".

"So this will take time, without mentioning the search and rescue operation and people that can still be under the rubble," he said.

"The hope here is that humanitarian aid can enter as soon as possible, but most importantly the search and rescue operation will find the largest number of people still alive."

According to the latest official toll, 21 people are confirmed to have been killed by Cyclone Chido in Mayotte.

But authorities fear that hundreds, and possibly even thousands, will be confirmed killed once the true scale of the toll is revealed after the rubble is cleared and roads are unblocked.

After hitting Mayotte, Cyclone Chido made landfall in Mozambique, claiming at least 34 lives and destroying 23,600 homes, authorities said.