WESTPORT - A pipe bomb exploded outside the house of well-known Westport conservationist Pete Lusk on Saturday night, destroying his letterbox and reinforcing his fears for his family's safety.

The 10.30pm explosion was heard blocks away.

"The letter box was blown to smithereens," Mr Lusk said.

"We did actually find the front, which is a little semi-circle of wood, that was on the other side of the street. That was even split and it had explosives all over it. It was all black and it smelled like gunpowder .

"It's a step up in the attacks we've had and you do wonder what the next one is."

The bomb went off during a thunderstorm, when Mr Lusk, his partner Carolyn and their nine-year-old daughter Danielle were in bed asleep.

Westport police sergeant Craig Tickelpenny said a teenager was seen running away after the explosion.

A second pipe bomb exploded behind Westport's Carnegie Library, in a public carpark, just before midnight.

Mr Tickelpenny said it was "a bit of a coincidence" the first bomb had been aimed at a well-known conservationist, but police had no evidence Mr Lusk's beliefs were the reason his home had been targeted.

Mr Lusk resigned as spokesman for West Coast Forest and Bird and the Buller Conservation Group (BCG) just over a fortnight ago, saying he feared for the safety of himself and his family.

He had represented BCG for more than 20 years and Forest and Bird for about eight years.

Today he had no doubt the bomb was retaliation for his green views.

"I can't see that we weren't the target -- I'm sure we were the target.

Mr Lusk said a car full of young men had followed and abused him as he was biking home about a fortnight ago.