MORONI, July 30 (Reuters) - At least 20 illegal migrants were feared drowned on Monday after their boat sank off Comoros en route to the French-administered island of Mayotte, residents said.

Kamaleddine Gharibou, director general of a hospital on Anjouan, one of Comoros' three main islands, said about 30 passengers including women and children were onboard the small fishing boat when it sank on Friday.

Seven survivors were brought to his hospital, Gharibou said, where four of them -- two Comorian men, a woman and a 5-year-old child from Madagascar -- later died.

"The bodies of the two Comorians have been buried according to Muslim tradition and the two Malagasy are in the Christian cemetery," he said.

Residents say hundreds of Comorians, Malagasy and mainland Africans die each year making the 50-mile (80 km) crossing from Anjouan to Mayotte, which is dangerous in bad weather.