Travellers are being given urgent safety warnings over the risks from malaria after deaths and serious illnesses among recent British visitors to the Gambia, west Africa.

Two people have died and two are seriously ill among six cases reported in the last month, and health watchdogs fear millions of others may be putting themselves in danger by going to around 100 countries worldwide where malaria is endemic without taking the necessary precautions before, during or after their visit.

People visiting friends and relatives, holidaymakers and business travellers are being urged to take tablets against the disease before arrival, wear suitable clothing, use insect repellent and sleep in mosquito-proof rooms or insecticide-protected nets. They are urged to see doctors quickly if they show flu-like symptoms after returning to Britain.

Returning Britons have accounted for most of the seven to 16 malaria deaths a year in this country, and up to 2,000 cases annually, in recent years.

Symptoms from the most dangerous malaria parasite plasmodium falciparum, carried by mosquitoes, can take 12 months to appear and blood tests are needed to distinguish the potentially fatal infection from influenza. In 2004, 31 travellers to the Gambia returned with falciparum infection and two died.

The Health Protection Agency (HPA) is concerned that travellers either do not get sufficient health advice from travel companies and tour operators or do not give it sufficient importance.

But the recent cases from the Gambia, involving five holidaymakers and one business traveller who had not taken appropriate anti-malarial medication, has prompted new warnings. The Association of British Travel Agents on Tuesday reminded its 1,700 members that its code of conduct required them to tell clients of health requirements for different destinations.

"It is essential that all tourists obtain advice before visiting a country where malaria is a hazard," it said in an email alert. The Federation of Tour Operators is also alerting members.

Around 5 million Britons a year travel to malarial areas around the world and up to three-fifths do not seek advice before going.

The Britons who caught malaria in the Gambia , a popular winter destination, were mainly staying in resorts within 12 miles of the coast and were aged between 31 and 61.