The president experienced "slow intestinal transit and abdominal distention" over a 12-hour period so doctors inserted the nasogastric tube -- meaning he would be fed through the nose -- according to a statement from Sao Paulo's Vila Nova Star hospital.

The bulletin, which said doctors would daily review when they could allow Bolsonaro to return to feeding orally, gave no details of when he might be discharged from hospital.

Bolsonaro, 64, underwent a five-hour operation on Sunday to repair an abdominal hernia.

The procedure took two hours longer than anticipated. It was his fourth operation since being stabbed in the stomach a year ago at a campaign rally.

On Monday, the president broadcast a video of himself on Twitter walking along a hospital corridor.

Bolsonaro is due to fly to New York later this month to address the UN General Assembly.