Voters in the Caribbean nation of St Vincent and the Grenadines are to decide whether to break their ties with Britain's monarchy, even as the Queen is making a visit to the region.

A two-thirds majority in the referendum is needed to adopt a proposed constitution that would replace the charter in place since independence from Britain in 1979.

If the charter is approved, St Vincent and the Grenadines would join other Caribbean nations that have enacted new constitutions in recent months, including the Dominican Republic and the Cayman Islands.

The proposed constitution would remove the Queen as head of state and create a president nominated by the two political parties. Among other changes, it would establish a new court of appeals to replace Britain's Privy Council, which is now the highest court of appeal for the island nation.

The country would remain a member of the Commonwealth.

The Queen Elizabeth, who visited Bermuda Tuesday, is in the region to attend a Commonwealth summit in Trinidad.

Elections supervisor Sylvia Findlay told local media there are 97,000 registered voters, but the list contains an undetermined number of people who have died or moved away.

Monitors from the 15-nation Caribbean Community, the Organisation of American States and the Organisation of Eastern Caribbean States will observe the referendum.