UPDATED 2.51pm: Two people have been rescued from the Waikato River after their kayak sank just before noon.

The pair were drifting towards the rivermouth, and firefighters commandeered a private boat to reach them opposite the Waiuku Forest.

The Coastguard also launched a vessel in a rescue operation that the police and ambulance service also attended.

"Someone on the shore called it in after they noticed the kayak had sunk and the people were in trouble," a Fire Service spokesman said. "A significant rescue operation was immediately put in place."

It is believed the two people were wearing lifejackets. Back on shore, they were assessed by ambulance staff to determine if further medical attention was necessary.

"By all accounts it could have been a very serious situation for the kayakers and it was fortunate they had lifejackets on," the Fire Service spokesman said. "The firefighters lifted them out of the water and they were suffering from mild hypothermia."