One person is dead and four more are badly injured following two separate car crashes near Thames this afternoon.

Motorists are being urged to avoid east of Thames on SH25 between Kopu Bridge and the Turua turn-off and SH25A, west of Thames.

Two cars collided at about 1.25pm on SH25 west of Kopu Bridge before the Turua turn-off and two people have been flown by helicopter to Waikato Hospital in critical condition.

Fire crew from Thames and Ngatea cut the two trapped motorists from each of their cars, Northern Fire communications shift manager Dallas Ramsay said.

One person later died, St John said in an alert.

About 15 minutes later on the other side of Thames a car carrying three occupants careered down a bank on Kopu-Hikuai Rd, between Kirikiri Valley and Puketui Roads.

The rescue helicopter is in also attendance and two people are in a critical condition, and another in a serious condition.

The Police serious crash unit is investigating both crashes and both SH25 between Kopu Bridge and the Turua turn-off and SH25A remain closed until further notice and motorists are urged to take alternative routes.