A Coach carrying 30 people and a black Mercedes were in collision on the A11 between the A1101 and the B1106 by the The Great War Memorial.
Suffolk Police say all 30 people on the coach appear to be fine. There were four people in the Mercedes, two are said to be critically ill.
It is believed that the other two passengers are fine. The air Ambulance has been called to the scene, together with the Suffolk Fire Service. Suffolk Police said it is not yet known how long the A11 closure will be in force.
Drivers are advised to avoid the area.
More top news
Rather cloudy with outbreaks of rain
The Duchess of Cambridge has praised the "amazing and life-changing" work of children's hospices in a touching and personal letter.
Cloudy, coastal drizzle later tonight. Breezy near the coast