By Nick Carey

HANNIBAL, Missouri (Reuters) - Lower flood crests brought welcome news to towns on Mississippi River on Thursday, but officials and workers on the front lines said the next few days will still be crucial as they fight to keep levees whole.

"You always have to be ready for the Mississippi to raise its ugly head," said John Hark, emergency management director for the city of Hannibal and Marion County, Missouri.

"It's a beautiful river, but it can turn very vicious and ugly in a hurry," he added. "Until that river goes back within its banks where it belongs, I'll take no chances."

Hannibal, boyhood home of author Mark Twain, is protected by an earth levee and flood wall, and it is not considered at risk. Shops in the picturesque downtown with its red brick and wood houses are open. The Twainland Express still takes tourists around town on a guided tour.

The U.S. Army Corps of Engineers said on Thursday that the river at Hannibal was at 28.4 feet and was expected to crest at 29.4 feet on Sunday. Flood stage is 16 feet. The record high was 31.80 feet during the last big flood in 1993.

Flood levels in the area were down one to two feet on Thursday as levee breaches upstream siphoned water away from the river.

Hark said his concerns were focused not so much on Hannibal but on the two levee districts that he oversees, where work continues on "shoring them up to improve our defenses."

Elsewhere along this stretch of the Mississippi that is seeing the overflows of last week's torrential rains in Iowa and further north, an army of volunteer workers was checking levees as the crest approaches.