PORT-AU-PRINCE, Haiti -- An intense search was underway Monday after 329 prisoners escaped from an overcrowded prison on the outskirts of the Haitian capital in an attack apparently aimed at freeing the son of a prominent businessman held on kidnapping charges.

Authorities increased security along the border and appealed for help from officials in the neighbouring Dominican Republic and in nearby Jamaica, fearing some of the men who escaped had already fled the country following the breakout.

In the Dominican Republic, the government ordered extra troops to its porous border with Haiti and were searching for any of the escaped prisoners, Defence Minister Sigrido Pared said.

Witnesses said about 15 gunmen in two SUVs showed up at the prison in Croix-des-Bouquets before noon on Sunday and opened fire on guards, wounding two. Haitian officials said the attack appeared to be timed to coincide with recreation time and prisoners began to riot as the shooting started.

The authorities are investigating whether there was co-operation from members of the Haitian police who guard the prison, Justice Minister Jean Renel Sanon said.

The attack was apparently intended to free Clifford Brandt, a member of a wealthy family, who has been awaiting trial since 2012 for allegedly running a kidnapping ring in the capital.

The government offered a reward equivalent to about $25,000 for information leading to Brandt's capture.

Police Chief Godson Orleus said 10 of the 329 prisoners have been recaptured.

The prison held 899 prisoners at the time of the attack, about 130 over capacity.