Mel Carnahan with his wife, Jean

The small plane crashed near Goldman, about 30 miles (50 km) south-west of St Louis, shortly after take-off.

Both Mr Carnahan and his son were licensed pilots.

Jefferson County Sheriff Glenn Boyer said human remains had been found at the crash site.

Wreckage hunt

The plane came down in a hilly, woodland area.

Some 100 searchers were hunting for wreckage in thick fog.

The governor had been expected at a campaign rally on Monday evening in New Madrid, about 150 miles south of St Louis.

Mr Carnahan was governor of Missouri for eight years. He has been locked in a tight race for the US Senate with incumbent Republican Senator John Ashcroft.

Mr Carnahan had been due to attend the third presidential debate between Vice-President Al Gore and Texas Governor George Bush in St Louis on Tuesday night.

Mr Gore telephoned Mr Carnahan's wife, Jean, after he heard the news of the crash.

Political career

Mr Carnahan won his first public election at the age of 26 as a judge in his hometown of Rolla. He served two terms in the Missouri House of Representatives and was later state treasurer.

In 1988, he was elected lieutenant governor and won the governor's office in 1992 and 1996.

In 1976, another Senate challenger in Missouri, Jerry Litton, died in a plane crash as he and his family were flying to a victory celebration the night he won the Democratic nomination.