RIYADH (AFP) - The Saudi health ministry on Sunday announced a new Mers death, raising to 55 the number of people killed by the coronavirus in the country with the most fatalities.

A 37-year-old Saudi man died in Riyadh, the ministry said on its website.

The World Health Organisation says it has been informed of 155 laboratory-confirmed Mers cases worldwide so far, including 64 deaths, most of them in Saudi Arabia.

Experts are struggling to understand the disease, for which there is no vaccine.

It is considered a deadlier but less-transmissible cousin of the Sars virus that erupted in Asia in 2003 and infected 8,273 people, 9 per cent of whom died.