MADRID/LISBON, April 28 (Reuters) - Power started returning to parts of the Iberian peninsula late on Monday after a huge outage brought parts of Spain and Portugal to a standstill, grounding planes, halting public transport, and forcing some hospitals to suspend routine operations.

Spain's Interior Ministry declared a national emergency and governments from the two countries convened emergency cabinet meetings as officials tried to find out what caused the mass blackout, which began around 1033 GMT. Outages on such a scale are extremely rare in Europe.