A Napier City Council spokesperson said they were unable to provide any information about his condition.
"Our heartfelt thoughts and very best wishes are with our Mayor, his wife Shirley and his family at this time.
Deputy Mayor Faye White will assume the role of Acting Mayor.
Dalton, who is in his late 60s, is in his second, and final term as Mayor of Napier.
The former stockbroker was elected to the role in 2012, and in the 2016 election ran unopposed.
He has served as a councillor since 2007.
He has presided over changes to the city including the Marine Parade redevelopment and allowing Easter Sunday Trading.
Upcoming projects supported by Dalton include a new pool, and the aquarium expansion.
Recently, he told Hawke's Bay Today he did not have any major plans after he hangs up the mayoral chains in October, but did say he was looking forward to spending more time with his family, especially his grandchildren.
