Nepal's King Birendra and Queen Aishwarya were among 13 members of the royal family shot dead by their son, Crown Prince Dipendra, during a row at the royal palace in Kathmandu yesterday, sources said.
The 29-year-old prince then turned the gun on himself, they said.
Army sources and sources close to the prime minister said 14 royals in total, also including Prince Nirajan and Princess Shruti, were killed in the massacre at the Narayan Hity royal palace during the family's regular Friday dinner.
There was no official confirmation of what occurred, or what the dispute might have been about.
An official announcement on the incident was expected this morning. However, according to recent newspaper reports, astrologers had advised the royal family that the crown prince, aged 30, should not be allowed to marry or produce children until after he was 35.
If this directive was not followed the king would die, the astrologers warned, according to the reports.
The 55-year-old King Birendra had ruled since 1972, as an absolute monarch until a constitutional monarchy was introduced in 1990.
One of the king's brothers, Prince Gyanendra, was understood to have been out of Kathmandu last night and was being brought to the capital by military helicopter.
If, as feared, most members of the immediate royal family had died in the massacre, he would accede to the throne.
The Nepali Times said the crown prince "reportedly shot his family with a semi-automatic". The newspaper quoted sources close to the royal family as saying the crown prince died in hospital early today after being operated on for a self-inflicted gunshot wound.