ANTANANARIVO (AFP) - Madagascar security forces were on Sunday investigating a grenade blast a day earlier that left a toddler dead and over 50 wounded just hours after the inauguration of the island's new president.

Police were still in the early stages of the investigation, police spokesman Florens Rakotomahanina told AFP, without giving any details.

A grenade explosion ripped through a crowded bus stop on Saturday just hours after President Hery Rajaonarimampianina had taken the oath.

The blast occurred some 200m from the stadium where Mr Rajaonarimampianina had been installed as the island's first elected president since a 2009 coup.

Medical officials said the numbers of injured had risen to 52 from 37 after more people turned up at the main hospital.

"The numbers increased a little... because more people came after hearing that the state would take charge of medical bills," said HJRA hospital director Jean Claude Razafimahandry.

But the majority of them had been discharged on Sunday, leaving 19 still receiving treatment.

The President visited the injured on Saturday, telling them his government would not tolerate any form of violence and vowing the perpetrators would be brought to justice.

A security source told AFP on condition of anonymity that a man on foot had tossed the grenade into a group of people outside the stadium and ran off.

The blast occurred a few hours after the inauguration ceremony that was attended by foreign dignitaries including heads of state from Namibia and the Indian Ocean islands of Mauritius and the Seychelles.

Taking the oath of office, Mr Rajaonarimampianina, 55, had called for national unity and reached out to his political rivals to help restore stability to the Indian Ocean island.

The Canadian-educated accountant won last month's elections that were aimed at restoring democracy and much-needed foreign aid to the island which was plunged into crisis by the coup.